Initial work of adaptive metrics aware routers, see #2547
ClusterLoadBalancingRouter and refactoring of metrics, see #2547

* MetricsSelector, calculate capacity, weights and allocate weighted
  routee refs
* ClusterLoadBalancingRouterSpec
* Optional heap max
* Constants for the metric fields
* Refactoring of Metric and decay
* Rewrite of DataStreamSpec
* Correction of EWMA and removal of BigInt, BigDecimal
* Separation of MetricsCollector into trait and two classes,
  SigarMetricsCollector and JmxMetricsCollector
* This will reduce cost when sigar is not installed, such as
  avoiding throwing and catching exc for every call
* Improved error handling for loading sigar
* Made MetricsCollector implementation configurable
* Tested with sigar
AdaptiveLoadBalancingRouter and more refactoring of metrics, see #2547

* Refactoring of standard metrics extractors and data structures
* Removed optional value in Metric, simplified a lot
* Configuration of EWMA by using half-life duration
* Renamed DataStream to EWMA
* Incorporate review feedback
* Use binarySearch for selecting weighted routees
* More metrics selectors for the router
* Removed network metrics, since not supported on linux
* Configuration of router
* Rename to AdaptiveLoadBalancingRouter
* Remove total cores metrics, since it's the same as jmx getAvailableProcessors,
  tested on intel 24 core server and amd 48 core server, and MBP
* API cleanup
* Java API additions
* Documentation of metrics and AdaptiveLoadBalancingRouter
* New cluster sample to illustrate metrics in the documentation,
  and play around with (factorial)
Merge branch 'master' into wip-2547-metrics-router-patriknw

Conflicts:
	akka-actor/src/main/scala/akka/actor/Deployer.scala
	akka-cluster/src/main/scala/akka/cluster/ClusterMetricsCollector.scala
	akka-cluster/src/test/scala/akka/cluster/MetricsCollectorSpec.scala
Incorparate review feedback, see #2547

* case object and case class for MixMetricsSelector
* Rename decay-half-life-duration to moving-average-half-life
* Clarification of decay-half-life-duration and collect-interval
* Removed Fields, Java compatibility issue
* Adapt for-yield variables
* Comment metrics collector constructor that takes system param
* Don't copy EWMA if not needed
* LogOf2 constant 0.69315
* Don't use mapValues
* Remove RichInt conversion
* sigar version replace tag in docs
* createDeployer factory method to make it possible to override
  deployer in subclass
* Improve readability of MetricsListener (in sample)
* Better startup of factorial sample (no sleep)
* Many minor enhancements and cleanups
Incorparate more review feedback, see #2547

* negative double check
* correction of cluster specification
* add isEmpty in WeightedRoutees
Fix failing WeightedRouteesSpec, see #2547
Add Typesafe repo in cluster sample, for sigar, see #2547
Hardening AdaptiveLoadBalancingRouterSpec, see #2547

* Problems with OOME for large heaps
* Create many small arrays instead of one large array
* Reduce half-life to get faster updates
-Xmx256m for multi-node jvms, see #2547
Simplify MetricsGossip and NodeMetrics merge, see #2547

* Also fixed problem with removed nodes potentially added
  back to MetricsGossip
Merge pull request #858 from akka/wip-2547-metrics-router-patriknw

AdaptiveLoadBalancingRouter and refactoring of metrics, see #2547