fixed leaking MethodOccurence objects
regex: fix handling of empty character class (which is not allowed in Java, Python & Ruby, but allowed in JavaScript)
Emmet: use editor preferred size in max size calculation
IDEA-82746 Disable "Push" button in Push dialog for Git when there is nothing to push

* HgPushOptionsPanel simplified;
* push button should not be disabled for hg single repo project, because we would like to push without loading commits
PY-13297 Use only PSI means to insert new line after comment