Some letters do not work in letter tablature entry mode (opposed to number entry mode)

- The current default setup for shortcut keys has a conflict between the 'H' assigned to the hairpin and the 'H' assigned to the 8th fret in tablature letter mode.
- There are defined tablature note entry actions only up to the 9th fret.

Fixes:

According to the suggestions in forum post http://musescore.org/en/node/25244, this patch implements the following fixes:

- Default shortcut key for haipin are changed into the more language-independent keys '>' and '<'.
- Actions for fret 10th - 14th are added, so they appear in the shortcut preference dlg box.
- No key is defined for these new actions (for analogy, they should be mapped to 'L' to 'P'), to avoid occupying several more letter keys in the general setup (note that 'N' and 'P' are already taken): the interested user has a known and simple way to define his own, if he has the need.
Merge pull request #829 from mgavioli/Fix_entering_letters_in_tablatures

Some letters do not work in letter tablature entry mode