Github: use httpclient4

* add ability to cancel network request by ProgressManager
Github: rewrite createPR

IDEA-120604, IDEA-120608, IDEA-120606, IDEA-120605
Github: cleanup
Github: add interruptable threads
Github: throw GithubCancelledException on empty response due to abort()
Github: make git-related tasks interruptable by ProgressIndicator
Github: cleanup
Github: do not propose to create remote again
Github: use volatile
Github: fix test
github: fix typo
github: do not try to cancel uncancelable
github: fix NPE
github: fix error string
github: remove duplicate setter
github: do not try to diff with non-configured remote
github: rename setter
github: fix typo
github: cleanup
github: cleanup