IDEA-108367 Idea hangs if try to merge with old branch from branches dialog

*merge action performed as background task (now not from awt)
* the problem appeared because of mercurial delete/modified conflict
cleanup
IDEA-97264 IntelliLang support for "Path to File" language
UpdateTo action from Branches view changed as Backgroundable
disable constant value warnings in complex assignments (IDEA-111478)
IDEA-111514Focus on filter text field in Add Action to Quick List window
IDEA-111500 Suggest the enclosing type as 1st element in return type suggestions list when creating the static method getInstance() of the singleton
javadoc on PropertyUtil.generate*Proptotype
CR-IC-1832 (explicit API)
IDEA-102173 Android XML: automatically insert app-level namespace when complete custom attrs instead of inserting it without an prefix
Github: IDEA-111284 description field can be null and this is not critical error
Github: use GitHub-generated html markup

* allow custom headers in PagedRequest