expose annotations of Segment to plugins
Bring Plugin save and load options and dialogs into line with score
saving and loading.
Correct plugin name default
Fix main layout memory leak
Fix score font memory leak
Fix TabScoreView memory leak
Fix M_new_divis memory leak
Fix QFontMetricsF memory leak
Fix Element memory leak
Fix icon action (char*) memory leak
Replace Shortcut key type char* with QString
Replace remaining char* strings in Shortcut with QString
Fix KeySym memory leak
Fix Clef elements memory leak
Check for corner case of self assignment
Fix M_def_rank memory leak
Bar lines: Fix custom span and generated management.

This PR should complete the revision of bar line flag managements.

- Make sure single bar line span changes affect both the `_customSpan` and the `_generated` flags.
- Make sure that manually bringing a custom-spanned bar line to default span resets the `_customSpan` flag and, if no other customization is in effect. the `_generated` flag.
- Deleting a measure bar line resets it to default configuration.
- Fix a missing initialization of `Measure::_endBarLineColor` variable.
- To simplify tests and debug, check boxes for the `BarLine::_customSpan` and the `BarLine::_customSubtype` have been added to the debugger dialogue box.

As far as system-initial bar lines are concerned, they were made un-editable by a recent commit (https://github.com/musescore/MuseScore/pull/1300). This PR add a few consistency changes:

- system-initial bar lines do not accept drops;
- they are not saved to score output files and are ignored when reading from them;
- their internal `_customSybtype` and _customSpan` flags are always false;
- they do not show up in the Inspector (if a system bar line is selected, the Inspector remains blank)

This PR DOES NOT include the special system-initial double bar management recently discussed. This will be part of a specific PR in the next days.

Together with previous PR's, this should ensure that:

- bar lines are written to a score output file only when some customization is in effect which cannot be reconstructed when reading back;
- any measure bar line can be edited;
- any measure bar line user edit is saved, written to the score file and read back properly;
- no system bar line edit is possible.
Refreshed optimized icons
Interface icons and minor icon tweaks
Fix `Measure::read()` as indicated by failing tests.