Allows to select the staff types for the instruments in the Instruments dlg box
Added support for "Add staff" and "Add linked staff" buttons
Add support for changing staff type(s) in "Create | Instr." dlg box to any defined type (either existing in the score or a preset)
Merge pull request #283 from mgavioli/Instrument_dlg_add_staff_types

Instrument dlg and wizard: add a combo box to staves to select the staff type