Accessible dialogs.

Added screen-reader feedback
Did tabbing orders and focus policies
Fix inspector focus shiftings
Merge pull request #1152 from andreituicu/accessible-dialogs

Accessible dialogs
fix typo
fix another typo
adjust/align smDrumset and gpDrumset

to the 'proper' names for GM- and GS Drum Sounds, see
http://anythingpeaceful.org/sonar/gm/gm-drums.html

Why neither smDrumset nor gpDrumsset is having the complete list
and
why we need to have both is beyond be though...
fix tests for drumsets
fix capitalisation and lose dashes
fix translation of context menu for time- and key sig
fix translation of staff group names
fix strings pre-translation in accessibilitsNames