Initial beta1 commit, extracted from signalfx-java

[agoallikmaa]

Initial commit for extracting signalflow from signalfx-java repository.

• New module is named signalflow-client, still published under com.signalfx.public group. Set version to 1.0.0-beta1 for now until a published version is tested.
• Kept nested structure of the modules, but the root project does not serve as the "parent pom" anymore since no other modules are expected to be public (but would still be possible without refactor if added for additional testing for example).
• Merged old connection and endpoint source files into signalflow-client module.
• All new source files are under package com.signalfx.signalflow.client which was previously unused by signalfx-java modules, so there should be no conflicts if for some reason some project includes both old and new modules.

[lachmatt]

LGTM

[breedx-splk]

Just for historical purposes, here's the list of files which originated above/outside the signalfx-signalflow submodule in signalfx-java:

• RetryStrategyTest.java
• RetryStrategy.java
• RetryHandler.java
• RetryDefaults.java
• AbstractHttpReceiverConnection.java
• SignalFxReceiverEndpoint.java
• SignalFxEndpoint.java

[breedx-splk]

Ignoring package and import lines, the files match the originals.