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

Don't store a pointer to ManagerImpl
Store a reference to audio preferences
Remove unused noisesuppression state

we're using one unique mainbuffer instance inside managerimpl
remove use of setErrorMessage(-1)
simplify audiodriver creation

move some code from managerimpl code

Almost all the callers of this method we're doing so already, those that
weren't now have try catch blocks where they use getSIPCall().