Implement "stg refresh --edit" again

Implement "stg refresh --edit" again

The -e/--edit flag to "stg refresh" was dropped between v0.13 and
v0.14, causing severe user dissatisfaction. This patch restores it,
along with -m/--message, -f/--file, --sign, --ack, --author,
--authname, --authemail, and --authdate.

I omitted the --committer options on purpose; I think they are a
mistake. Falsifying the committer info is not a common operation, and
if one wishes to do it for some reason, one can always set the
GIT_COMMITTER_* environment variables.

Signed-off-by: Karl Hasselström <kha@treskal.com>