remove unused functions

Update audio filters accordingly

remove unneeded class members
fix a bug with samplerate

same fix than [1519fc4d], for transfer button this time

use pa_stream_begin_write() when writing to speakers

simplify alsalayer xrun
split audio mainloop into smaller specific functions
simplify pulse audiostream
remove unused pulse functions

Fix a deadlock when closing the error dialog
Remove unused functions

Move ALSA specific options to alsalayer only

inline error signaling in the one alsa function using them