Remove "edit" links and forbid editing of non-custom levels
Set match/multi levels editable
show play/stats admin links for non-editable levels
Align editable and non-editable puzzles in user_stats view
Fix various issues, get all tests to pass
Merge pull request #1194 from code-dot-org/forbid_modify_default_levels

Remove "edit" links and forbid editing of non-custom levels