Fix 25423 - Issues with staff types in parts

Fix 25423 - Issues with staff types in parts

Issues:
- Creating part(s) for a score adds a whole set of staff types for each created part
- Editing staff types gives unexpected results in part staves and may cause crash

Fixes:
- New staff types are created only for the root score, not for linked parts
- When staff types are edited, the updated staff types are set into the root score staves as well as in the staves linked to them.

Link to issue: http://musescore.org/en/node/25423

**Note**:
I expect that this fix may invalidate some tests which use parts and have been created recently, as the  new scores created when running the tests will not have the extra staff types generated by parts in the ref scores. These tests will need to be fixed manually.