**Motivation**
Ribbon makes heavy use of Archaius in a static manner for configuration.  This pattern couple Ribbon with legacy archaius and its dependencies and makes it hard to run tests in parallel. By decoupling from both archaius and statics users can now provide alternative configuration mechanisms as well as improve testability.

**Changes**
- Introduce a new DynamicPropertyRepository abstraction to decouple from Archaius specific APIs
- For legacy support make the ArchaiusDynamicPropertyRepository discoverable via the service loader.
- Allow a non-static DynamicPropertyRepository to be associated with a IClientConfig.  This is a bit of a hack but minimizes code changes.
- Decouple all build.gradle dependencies from archaius, except for the ribbon-archaius subproject
- Pick up @zone from DynamicPropertyRepository and NOT from archaius's DeploymentContext
- Remove configuration for PollingServerListUpdater as it is not used and would always require static configuration

Make the object creation mechanism during client creation pluggable for better integration with DI containers.

Decouple core library from archaius1

**Why?**
Archaius1 is a deprecated library that also promotes static access patterns.  This PR is a first step of many to first decouple the library.  Subsequent PRs will address static access patterns.

**How?**
- Upgrade from Java 1.7 to 1.8
- Move all archaius specific code into ribbon-archaius
- Static ClientConfigFactory discoverable via the ServiceLoader
- Add default values to IClientConfigKey

Change BaseLoadBalancer to choose the LoadBalancerStats class based on a new ClientConfigKey so that a different impl can be used

(take 2 of) Adding eureka aware Loadbalancers that make use of new notification mechanism from eurekClient

Modifications:

Renamed ReceiveBuffferSize to ReceiveBufferSize

This is not backwards compatible if there's people using this configuration already.

Motivation:

`CommonClientConfigKey.PrimeConnectionsClassName` is typed as `IClientConfigKey<Boolean>`
which is incorrect since it must be a `String`

Modifications:

Make `PrimeConnectionsClassName` a constant of type `IClientConfigKey<String>`

Result:

Fixes #207

Support for exponential back off in response to HTTP throttle responses 502, 503, 504
Configuration property BackoffInterval to use as the interval for the default exponential back off strategy.  Default is 1000 msec.
Pluggable API to specify custom backoff strategy
Pluggable API to specify custom conversion of HTTP responses to exceptions

Changed IClientConfig interface. Move ClientConfigBuilder to be an inner class of IClientConfig. Added example of load balancing using URLConnection.

Change rxnetty version to 0.3.6. Implementation of ResourceGroup. Change to ConfigurationBasedServerList to make the server list part of client configuration.

- Added ribbon-rxnetty module for asynchronous HTTP communication based on Netty and RxJava
- IClientConfig and IClientConfigKey supports typed property
- Updates to serialization factory and serializer interfaces (replaced Guava TypeToken with TypeDef in the interfaces)
- Updates to HttpRequest and HttpResponse interfaces with addition of HttpHeaders

This reverts commit 5f62ec1f.

Support for async communication using Apache's HttpAsyncClient. Added streaming interface. Added support for Observable.