BUG-3128: Update RPC router concepts
Enrich DOMRpcImplementation with invocation cost, which is taken into account
when deciding which implementation to invoke. This allows local RPCs to be
prioritized over remote ones.
Also add the ability to filter implementations when notifying availability
listener. This allows remote RPC to filter its own registrations, preventing
re-forwarding loops, where a remote implementation would be forwarded as
a local one.
Change-Id: Id1d78d5031904e19134c103e12b79d68cf0b98c3
Signed-off-by: Robert Varga <rovarga@cisco.com>