Use internal templates to simplify minor formatting commands.

Use internal templates in getChangeMessageThreadId, and to set
the listId headers.  These are not admin editable templates
(they are not in files), they simply make the code a bit more
readable and editable at very little cost since we already
support velocity templating in emails.  Additionaly, factor
out the fromline creation to its own function.

Change-Id: I197b239e657e1dd604b07510c4430675f05d84eb
2 files changed