Improved TAB note entry and shortcuts

*) Fret note entry, string and chord navigation with easier shortcuts.
*) Comments out MuseScore::enableInputToolbar() code to avoid conflicts with actions linked to toolbar (select pad note value and rest).
*) Swap actions "pitch-up/down" and "pitch-up/down-diatonic" for TAB's.
*) Add [Shift][#] and NumPad [#] shortcuts for pad note value selection.
*) Keep "pad-note-...-TAB" shortcuts always disabled and "pad-note-..." actions always enabled in all input modes.
*) Key sequences for "pad-note-...-TAB" shortcuts are swapped into "pad-note-..." actions when entering TAB entry mode and original key sequences restored when leaving it, to have note entry tool bar buttons active in TAB entry mode.

For more details, see post(s) on dev mailing list: http://dev-list.musescore.org/Help-with-shorcuts-tp7577975p7578002.html