Fix #20826 - Numpad numbers no longer work to select note duration.

Fixed by blocking the creation (and pooling) of QAction creation for shortcuts with multiple alternatives in different states (like the 'common' and TAB-specific variants of "pad-note-..." shortcuts)

A rather detailed description of the implementation (regarding both the original, faulty, implementation and this fix) has been added to the mscore/shortcut.h file
Fix crash when displaying shortcut preferences
Add support for "NumPad" qualifier in textual representations of key sequences both in dlg boxes and in xml files.

Also allows to remove the <code> tag from shortcuts.xml
fix #20904: Not possible to enter a - or space in lyrics via Ctrl key
fix #20916: Importing 1.x score containing no measure causes crash
new grouping implementation, dialog for changing grouping for a timesig
fixes for timesig dialog
fix #20475
Merge pull request #315 from mgavioli/Fix_20826_Numpad_note_duration_shortcuts

Fix #20826 - Numpad numbers no longer work to select note duration.
Fix #20915 - Weird behaviour of "Reset to default" buttons in "Preference | Shortcuts"

The loadDefaultShortcuts() function in mscore/shortcut.cpp was not populating the list it returns.

Also:
- Made labels for "Reset to Default" buttons more explicit.
- Added (temporarily?) support for the <code> tag to loadDefaultShortcuts(), until the patch with "NumPad" support is merged (pull request 315), which makes the <code> tag obsolete.
fix for seek
fix sequencer regression
another try to fix sequencer
Some code clean ups.
Merge pull request #320 from mgavioli/Fix_20915_shortcut_reset_to_default

Fix #20915 - Weird behaviour of "Reset to default" buttons in "Preference | Shortcuts"