Moved most of paste code from scoreview to score.cpp into cmdPaste.
Removed copied code from tst_copypaste
Changed paste staff function to take a segment as a parameter
Changed assert to qAssert
Changed tst_copypastesymbollist to use the new cmdPaste in paste.cpp
Merge pull request #976 from BartlomiejLewandowski/paste-test

Paste refactor