Make days_ago a little more consistent

Rename days_ago to days for conciseness, and make the default interval
the same on all pages (14 days). It can be overridden with a query
string parameter if desired (previously this only possible on the
commit_stats page; it's now possible on profile pages as well).

Change-Id: I962cde2d8ae3f7d4ea6252240d311d1d85936089
Reviewed-on: https://gerrit.causes.com/24908
Reviewed-by: Greg Hurrell <greg@causes.com>
Tested-by: Greg Hurrell <greg@causes.com>
Replace a repeated hard-coded number with a constant

For robustness.

Change-Id: I0605145a2e96ee4bebd77d7a70d5239f783a7c7f
Reviewed-on: https://gerrit.causes.com/24909
Reviewed-by: Greg Hurrell <greg@causes.com>
Tested-by: Greg Hurrell <greg@causes.com>
Replace individual twigg-* executables with single twigg command

Instead of separate `twigg-app` and `twigg-stats` commands, we now have
a single `twigg` executable with subcommands, similar to many popular
command-line tools (like `git`, `gem`, `bundle` etc).

This commit moves the functionality of the original commands into
separate files, split up in such a way as to facilitate testing and make
future extension easy (for example, I anticipate adding `pivotal` and
`gerrit` subcommands).

Adds a `help` subcommand as a bonus.

Change-Id: Ia7c9ae1e16f9713eff504e99417dbeb7343fe18a
Reviewed-on: https://gerrit.causes.com/24910
Reviewed-by: Greg Hurrell <greg@causes.com>
Tested-by: Greg Hurrell <greg@causes.com>
Show aggregate line count stats for `twigg stats -v`

Much as we show a total count of commits for all authors (collectively),
we now show a total count of lines added and deleted. We could also do
this at the per-author level in the future, although that will be a
subject for another commit.

Change-Id: Ib211a86e528895d1a04d5ed28a0dccc368059570
Reviewed-on: https://gerrit.causes.com/24911
Reviewed-by: Greg Hurrell <greg@causes.com>
Tested-by: Greg Hurrell <greg@causes.com>