DiffEditor: Save description along with diff.

Save complete, git-applicable patch when saving the result of
for example 'git show'. Strips some Creator-specific tags
off the description and reformats the description such
that it is accepted by git.

Change-Id: I739d85a7263f97e2149a2794974ba026f2eca067
Reviewed-by: Orgad Shaneh <orgads@gmail.com>