(bug 43606) more selenium tests for statements UI

- multiple statements
- multiple claims for same statement
- check values & links after reload
- check behavior of entity selector when editing a property value
- check RETURN & ESCAPE key behavior
- removing claims
- separate tests for commons media type
- separate tests for item type

Change-Id: I12099ff8495154d0589a226ceb943767b6c2eaea
Merge "(bug 43606) more selenium tests for statements UI"