Fix #23371 : in TAB's grace chords are not fretted at all or fretted incorrectly.

Since the grace chords have been moved from a parent segment of their own to a parent chord, the fretting algorithm no longer 'sees' them correctly.

Fixed by extending the fretting algorithm to deal with chords not belonging to segments.
Merge pull request #528 from mgavioli/Fix_23371_TAB_grace_chords_fretted_wrongly

Fix #23371 : TAB - grace chords fretted incorrectly
more strings cleanup
fix upper case of elementName in UI
more string cleanup
fix #23384: < character lost from stave text when loading file created in Musescore 1.3
Fix post 23402: note dragging in TAB

In TAB's, when notes are dragged, for instance, above an already occupied string, other notes were not re-fretted.

See http://musescore.org/en/node/23402 for an example.
Merge pull request #530 from mgavioli/Fix_post_23402_TAB_note_drag

Fix post 23402: note dragging in TAB
Fix #23406: Crash on copying multiple selected chord names.

The map key used to sort by track and tick the elements to copy overflowed.
Merge pull request #531 from mgavioli/Fix_23406_Crash_on_chord_names_copy

Fix #23406: Crash on copying multiple selected chord names.
move qt for ci tests
Add file exists function for plugins
Merge pull request #532 from vgstef/PluginFileIO

Add file exists function for plugins
When multiple staff-collateral elements are selected, copied and pasted, they are pasted according to the note (chord) count of the original passage rather than according to the tick distances.

This makes sense for all the supported element kinds, except chord symbols.

Corrected to paste chord symbols according to source tick distances. If a chord symbol falls on a tick where there is no SegChordRest segment, such a segment is created.
fix #23366

Yet another and probably still not the last...
Attempt to fix workspaces

but I'm affaid more work is needed for those
Merge pull request #533 from mgavioli/Fix_23457_chord_symbol_copying

Fix #23457 : Chord symbol copying
Merge pull request #534 from Jojo-Schmitz/orig.text

Some more fixes for #23366
Fix #23447 and #21577 : Adding or removing a time sig deletes key changes in the affected score span

The function TrackList::write(), which restores a score span after reworking the measure affected by the time change, ignores key sig changes. Corrected.

As key sigs have to be placed at measure beginning, an existing key sig which, with the new time subdivision, would be placed mid-measure is moved at the beginning of the measure it falls into.

Note: this may e not round-trip safe; i.e. if a time signature which alters measure boundaries is added and then (manually) removed, key signatures may end up at different points than originally. Undo, however, works as expected.
Merge pull request #535 from mgavioli/Fix_23447_adding_removing_timesig_at_keysig_change

Fix #23447 and #21577 : Time sig addition and deletion and key sigs