notifications: proper check for test messages

polymer: initialize as soon as possible

polymer: introduce webcomponents to rhodecode

release: merge back stable branch into default

Added tag v4.3.1 for changeset 0e4dc11b58ca

release: Finish preparation for 4.3.1

release: updated pip2nix output for 4.3.1

release: Start preparation for 4.3.1

ux: show list of causes for vcs unavailable error page

vcs-error: replace disable_vcs middleware with vcs and http exceptions to avoid vcs connection errors showing to the end user fixes #4140