Use libuv for almost all concurrency

* Free D2D frontend from VCRT concurrency
* Removed all thread includes and uses
* Remove some mutexes
* Replace future for library membership test
* Fix case for LockGuard to lock_guard
* Add uv helpers to PCH for now
* Replace Asio workers and threading
* Replace std recursive_mutex with Boost for now
* Implement own recursive_mutex, generalize lock_guard
* Fix excessively unlocking recursive unlock
* Re-enable Asio worker pool for file processing
Bump version to 0.2.41
Merge branch 'release/0.2.41' into develop