Initialize espeak in async playback mode and explicitly synchronize after each synth operation in the worker thread.

- All resources are either under src or under resources dirs
- Removed files top level directory
- Move flightgear files to top level dir

Plus a large number of other changes to allow for orderly shutdown of
objects without crashes or asserts. This is need for unit tests to
create/delete global state around every test.

This reverts commit 4d033715.

Move Windows sound API to right thread context and make it an object member. Perform init within the right thread context. Add capability to play .wav files in addition via QMultiMedia