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
Added `cross_fields` mode to multi_match query

`cross_fields` attemps to treat fields with the same analysis
configuration as a single field and uses maximum score promotion or
combination of the scores based depending on the `use_dis_max` setting.
By default scores are combined.

Relates to #2959