scroll REST API should support source parameter

As stated in documentation, we should support `?source=` parameter in `/_search/scroll` REST operations.

This is how to reproduce it:

```sh
curl -XDELETE "http://localhost:9200/test"
curl -XPOST "http://localhost:9200/test/type/1" -d'
{
    "foo": "bar"
}'

# This one works
curl -XPOST "http://localhost:9200/_search/scroll" -d "FAKESCROLLID"

# This one gives: {"error":"Failed to derive xcontent from org.elasticsearch.common.bytes.BytesArray@0"}
curl -XGET "http://localhost:9200/_search/scroll/?source=FAKESCROLLID"
```

Closes #4941.
Add throttling to snaphost and restore operations

Closes #4855
fixed date_/histogram aggregation documentation - added documentation for the `min_doc_count` setting

Closes #4944
Fix javadocs for DeleteResponse.isFound()
fixed a bug where when executing on a single shard and sorting terms agg based on sub metric agg, the order (asc/desc) is not respected
 - fixed tests for terms order

Closes #4951
REST Get Field Mapping API: Fix NPE if field not existent

When fixing #4738, a small issue leaked into the implementation.
The equals check in the RestAction only applied when the master node
returned the rest request, otherwise the object equality would not hold
due to being transferred over the wire and being deserialized into
another object (from and an equality point of view) than the
FieldMappingMetaData.NULL object - this could result in serialization
exceptions as an empty length bytes reference is used in toXContent.
Add version to plugins

Plugin developpers can now add a version number to their es-plugin.properties file:

```properties
plugin=org.elasticsearch.test.integration.nodesinfo.TestPlugin
version=0.0.7-SNAPSHOT
```

Also, for site plugins, it's recommended to add a `es-plugin.properties` file in root site directory with `description` and `version` properties:

```properties
description=This is a description for a dummy test site plugin.
version=0.0.7-BOND-SITE
```

When running Nodes Info API, you will get information on versions:

```sh
$ curl 'http://localhost:9200/_nodes?plugin=true&pretty'
```

```javascript
{
  "ok" : true,
  "cluster_name" : "test-cluster-MacBook-Air-de-David.local",
  "nodes" : {
    "RHMsToxiRcCXwHiS6mEaFw" : {
      "name" : "node2",
      "transport_address" : "inet[/192.168.0.15:9301]",
      "hostname" : "MacBook-Air-de-David.local",
      "version" : "0.90.0.Beta2-SNAPSHOT",
      "http_address" : "inet[/192.168.0.15:9201]",
      "plugins" : [ {
        "name" : "dummy",
        "version" : "0.0.7-BOND-SITE",
        "description" : "This is a description for a dummy test site plugin.",
        "url" : "/_plugin/dummy/",
        "site" : true,
        "jvm" : false
      } ]
    },
    "IKiUOo-LSCq1Km1GUhBwPg" : {
      "name" : "node3",
      "transport_address" : "inet[/192.168.0.15:9302]",
      "hostname" : "MacBook-Air-de-David.local",
      "version" : "0.90.0.Beta2-SNAPSHOT",
      "http_address" : "inet[/192.168.0.15:9202]",
      "plugins" : [ {
        "name" : "test-plugin",
        "version" : "0.0.7-SNAPSHOT",
        "description" : "test-plugin description",
        "site" : false,
        "jvm" : true
      } ]
    },
    "H64dcSF2R_GNWh6XRCYZJA" : {
      "name" : "node1",
      "transport_address" : "inet[/192.168.0.15:9300]",
      "hostname" : "MacBook-Air-de-David.local",
      "version" : "0.90.0.Beta2-SNAPSHOT",
      "http_address" : "inet[/192.168.0.15:9200]",
      "plugins" : [ ]
    },
    "mGEZcYl8Tye0Rm5AACBhPA" : {
      "name" : "node4",
      "transport_address" : "inet[/192.168.0.15:9303]",
      "hostname" : "MacBook-Air-de-David.local",
      "version" : "0.90.0.Beta2-SNAPSHOT",
      "http_address" : "inet[/192.168.0.15:9203]",
      "plugins" : [ {
        "name" : "test-plugin",
        "version" : "0.0.7-SNAPSHOT",
        "description" : "test-plugin description",
        "site" : false,
        "jvm" : true
      }, {
        "name" : "test-no-version-plugin",
        "version" : "NA",
        "description" : "test-no-version-plugin description",
        "site" : false,
        "jvm" : true
      }, {
        "name" : "dummy",
        "version" : "NA",
        "description" : "No description found for dummy.",
        "url" : "/_plugin/dummy/",
        "site" : true,
        "jvm" : false
      } ]
    }
  }
}
```

Relative to #2668.
Closes #2784.
The forceful no cache behaviour for range filter with now date match expression should only be active if no rounding has been specified for `now` in the date range range expression (for example: `now/d`).

Also the automatic now detection in range filters is overrideable by the `_cache` option.

 Closes #4947
 Relates to #4846
Improve boolean handling in snapshot/restore request parsing

Fixes #4949
Randomized number of shards / replicas & add mapping for numeric fields
filtered query parses _name incorrectly
fixes #4960
Added benchmark for scroll searches.
The binary field shouldn't be stored by default, because it is already available in the _source.
Added missing licence header
[TEST] Added ability to skip REST test suite/sections based on their required features

As we have different runners for the REST tests we need a mechanism that allows us to add features to any of them without breaking all others builds.
The idea is to name a feature and temporarily use skip sections that mention the required new features, so that runners that don't support it will skip the test.

Added support for `features` field in skip section.
Added `Features` class that contains a static list of the features supported by the runner. If a feature mentioned in a skip section is not listed here, the test will be skipped.
[TEST] clarified skip features usage
Add explanations for all AllocationDeciders

Relates to #4380
Relates to #2483
Remove support for boost in copy_to field

Currently, boosting on `copy_to` is misleading and does not work as originally specified in #4520. Instead of boosting just the terms from the origin field, it boosts the whole destination field.  If two fields copy_to a third field, one with a boost of 2 and another with a boost of 3, all the terms in the third field end up with a boost of 6.  This was not the intention.

  The alternative: to store the boost in a payload for every term, results in poor performance and inflexibility. Instead, users should either (1) query the common field AND the field that requires boosting, or (2) the multi_match query will soon be able to perform term-centric cross-field matching that will allow per-field boosting at query time (coming in 1.1).
Don't load CompetionTerms if lookupFactory is null

Closes #4970
Closes #4788
Prevent usage of object based RamUsageEstimator in Completion090PostingsFormat