Show error message when the commentlink is configured wrongly

When the 'commentlink.<subsection-name>.match' is configured wrongly,
e.g. invalid regular expression, the change screen cannot be loaded,
and there is no error message or log.

Show an error dialog.

Bug: Issue 2514
Change-Id: Ie36fcdb0be13690cacaa64e235a08d7913dea937
Make the message of 'Cherry Picked' informative

The message reads:

 "This patchset was cherry picked to change: <Change-Id>"

This is not very informative, since the Change-Id is identical
to the current change.

A better message would be:

 "This patchset was cherry picked to branch <branch name> as commit <SHA1>"

Bug: issue 2513
Change-Id: I8bfb61b1a314cf2a985df7a571bb28e3f6cb49d4
Update 2.8.2 release notes

Change-Id: Iaf3f4ca1a45df7104e87491c5c223c4046f92ae9