* move protocol.rs into subfolder
* add trait for mocking network behavior
* add a mock version of network ops
* remove some redundant parameters from service messages
* ensure fetching erasure chunks automatically cancels
* introduce dummy ProvideRuntimeApi
* abstract over gossip somewhat
* add mock gossip handler
* skeleton test
* remove dependence of shared table on router
* remove worker dependence on its own sender
* test shutdown
* add tests
* test that gossip streams are cleaned up correctly
* refactor worker out into its own struct and reduce bound on executor
* remove reliance of tests on global thread pool