piano: Check for libgcrypt errors

Fixes mysterious segfaults from issue #369 and #293.
Add keyboard shortcut to reset volume

Closes #377.
Merge remote-tracking branch 'promy/master'

Conflicts:
	src/settings.h
	src/ui_act.h
	src/ui_dispatch.h
Merge branch 'master' into dl

Conflicts:
	src/settings.h
	src/ui_act.c