Changes include:
- Introduce an IpcSend trait to abstract over a collection of IpcSenders
- Implement ResourceThreads collection to abstract the resource-related
sub threads across the component
- Rename original ResourceThread and ControlMsg into an unifed CoreResource__
to accommodate above changes and avoid confusions
It's a pointless abstraction that propagates the obsolete chan terminology,
swaps the order in which the sender and receiver are returned, and hides a
source of panics.
