gists: Remove gist_type from update method in model. #4243 We do not allow to change the gist type from public to private or vice versa. Therefore there is no need to provide a ability in the model to do it.

imports: Remove unused imports.

tests: Adapt tests to recent changes in vcs lib.

pyro4: Add the custom header `X-RhodeCode-Backend` to the pyro4 backend responses. This custom header sets the SCM backend which is in use. It is used to identify VCS responses in the error handler. VCS responses are skipped during error handling.

settings: new and improved server announcements fix #676 #1342 #4121

pr: Use unicode object when generating the pull request title

events: use branch from previous commit for repo push event commits data so that grouping works, fixes #4233

channelstream: try to use proxy url's unless ws urls are not explictly defined

tests: Add a test that checks return type of pr title generate function. (has to be unicode)

pr: Use unicode object when generating the pull request title