Pulled explodePath() up into AbstractHttpQuery. Made getQueryBaseRoute()
abstract.
Updated comments to indicate HttpRpc is for built-in RPCs only.
Updated copyright on AbstractHttpQuery's header.
Query object for use with HTTP RPC plugins.
Base class for HTTP RPC plugins.
Major refactoring of RpcHandler to support HTTP RPC plugins.

Moved the management of all RPC-related plugins into new manager class
which gets handed to RpcHandler on construction.
Removed management of RpcPlugins.

These are now managed by RpcPluginsManager.
PipelineFactory now creates RpcPluginsManager.
Added new Java files to Makefile.am.