Any instrument which does not have string data is given a default guitar-like string set.

Changed to a default empty string set.

This also allows to filter out TAB staff types in staff props dlg box for an instrument without strings defined.
Merge pull request #348 from mgavioli/remove_guitar_as_default_tablature

Remove guitar as default string set
update icons, now white
Instrument Wizard (incl. New score Wizard):

Staff type presets listed in the preset combo boxes are filtered out according to instrument data:

- if has string data, allow normal and tab presets
- if has drum set, allow percussion presets only
- if has neither, allow normal preset(s) only

Also:

Staff Props dlg box: completes filtering out of perc. staff types (and fixes two bugs!)
STAFF PROPERTIES dlg box:

Hide string data controls if the staff instrument has no strings.
Merge pull request #350 from mgavioli/Instr_wizard_filter_staff_types

Instrument Wizard: filter staff presets according to instr. data
add namespace Ms
Merge pull request #351 from mgavioli/STAFF_PROPS_hide_str_data_controls

STAFF PROPERTIES dlg box: Hide string data
fix regression tests
fix build on windows
fix build on Mac OSX
removing a duplicate entry in instriments.xml

and fixing a typo
updating instr_language.xml

to match the latest version of instruments.xml
fix #20991 : Ledger line of normal note shortens if small note is above
Merge pull request #352 from Jojo-Schmitz/instruments.xml

Instruments.xml
Fix #21069 - Opening the "Create | Instruments.." dlg box causes crash.
Merge pull request #353 from Soerboe/fix20991

fix #20991 : Ledger line of normal note shortens if small note is above
Merge pull request #354 from mgavioli/Fix_21069_Instr_wizard_crash

Fix #21069 - Opening the "Create | Instruments.." dlg box causes crash
factorize mac head width computation in Chord