Replace foreach with for.
Remove java-style iterators.
Don't mix const iterators with non-const ones.
Use std algorithms when possible.
Fix const correctness.

Change-Id: I6519e490b6270f56b54f05867c6def5f140e57cd
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Karsten Heimrich <karsten.heimrich@qt.io>