Add a new CommentLinkInput class in the extension API, and include it
in the ConfigInput as a map of commentlink names to CommentLinkInput.
Each entry in the map is added or updated in the project's config. If
the config already contains a commentlink with the same name, it is
updated with the values supplied, otherwise it is added. If the map
contains a null value, that entry is removed.
Since commentlinks at project level may not supply the 'html' value,
this is not included in the input.
Now that we are able to set commentlinks via the API, also expand the
tests to cover the behavior of project specific commentlinks together
with globally configured commentlinks, and inheritance of commentlinks
from the parent project.
Change-Id: Ief84c2f3bb85c6fcb28ccb1c09c537f6ab75395a
67c8f1454c