Convert 3 email classes to file based templates.

Convert the NewChange, RegisterNewEmail and ReplacePatchSet
classes to use file based velocity templates which an admin
may edit.  Factor out getChangeDetail and getReviewersNames
from formatChangeDetail and formatSalutation respectively
to enable this.

Change-Id: I36aa7051f06c7641114e2e681639267769846c22
9 files changed