Change some declarations from 'struct' to 'class' (and vice-versa)
allow to load/save default session-properties
add a generic Option Editor Component for stateless widgets
add 'save defaults' option to properties dialog
re-arrange tabs in Session > Properties dialog (Misc is last)
update ARD - allow to release it as standalone tool.

see https://github.com/x42/alsa_request_device
Merge branch 'cairocanvas' into recfolder

No further development on 'recfolder' is planned (hence merge).
The first commit (5edbb2cb) can be rebased for a short to mid-term
solution. Mid-to-long term the general raid and file management
situation will need to be addressed in a more consistent and
creative manner.

Conflicts:
	gtk2_ardour/session_option_editor.cc
	gtk2_ardour/session_option_editor.h