TAB entry mode: Sync current note with string cursor.

In TAB entry mode, while moving the string cursor up or down, the current (selected) note remains the last inserted note, with the following inconsistency:

- new notes are entered at the string cursor
- but cmds affecting a note (pitch up/down and like) changes the selected note;

this is likely to lead to confusion and unexpected results.

With this fix, when the string cursor is moved up/down and a note is found at the new string, it is made current (selected). If there is no note, the selection remains unaffected.

Note: Also corrected a typo in the name of a StaffType method.
Merge pull request #1016 from mgavioli/Sync_strg_cursor_and_curr_note_in_TAB_entry_mode

TAB entry mode: Sync current note with string cursor.