Staff props and stafftype props dlg box redesign

Re-design staff props and staff type props dlg boxes.

- Staff props dlg: added type props common to all types (num. of lines, line dist., etc.).
- Changing some type props but canceling the main dlg no longer changes the staff type.
- Fixed equality checks in `EditStaff::apply()`.
- `EditStaffType` dlg: removed group selector and added a preset selector + re-organized dlg layout
- Preset list dlg: removed, as now included in `EditStaffType`.
- Both dlgs: set all buddies and proper tab order.

Also:
- Staff group names ("Standard", "Percussion", "Tablature") made uniform in spelling and translatable.
- Fixed `Instrument::operator==()`.

A preview of the new dlgs can be seen at: https://www.dropbox.com/s/xtxnjnututg97e5/staff_stafftype_props_dlgs.png

Comments welcome.