[CS] Use Celluloid's thread pool for CallControllers
[CS] Use Celluloid::ThreadHandle for pool safety
Merge branch 'release/2.3.4' into develop
[BUGFIX] Fix race condition in barging in before output start is acknowledged

When doing interruptible output, don't start the input component until we have a handle on the output component. This prevents us trying to stop an output component which we don't have a ref for yet.
Merge branch 'feature/controller_thread_pool' into develop
[FEATURE] Do a stack dump when receiving USR1
[DOC] Changelog entry
Revert "[FEATURE] Do a stack dump when receiving USR1"

This reverts commit dd4d3927621721cd53c6ab5c024f2323db4a8390.
[UPDATE] Bump to 2.3.5
Merge branch 'release/2.3.5'