drop DB rules
Preclude adding stub participants as team members. Resolves #2364
add Bountysource badge
directly link to building.gittip from the README
Move untip.py to a method on Participant

This is a step on the way to making account cancelation self-serve. This
commit keeps the untip.py script used in the current cancelation process
but delegates to a (tested) method on Participant.
Add link to credit card update page on expiry notifications.
Merge pull request #2471 from gittip/2471-cc-notification-link

Credit card expiration banner needs a link to setting
Merge pull request #2464 from gittip/clear_tips_receiving

Move untip.py to a method on Participant
This factors out an archive method from take_over

Right now we archive participants during take_over, but we also want to
archive participants during account cancelation.
Merge pull request #2465 from gittip/factor-out-archive

Factor out archive
Smooth out take_over tests

Change from `alice_participant` and `alice` to `alice` and
`alice_twitter`. Makes it easier to reason about participants vs.
accounts elsewhere if we use this nomenclature.
Merge pull request #2466 from gittip/smoother-tests

Smoother tests
This test gives us 100% coverage of take_over

That doesn't mean there aren't any bugs, of course. :-(
Merge pull request #2467 from gittip/cover-take_over

This test gives us 100% coverage of take_over
Refactor reserving a username

There's actually a bug in this, we get an InternalError when the first
username attempt is taken and we try a second one. I don't have time to
debug that right now. At least the code is deduped now.
Merge pull request #2468 from gittip/refactor-reserve-username

Refactor reserving a username
Add some constraint checking to archive

This makes it suitable for use during account cancelation.
Merge pull request #2469 from gittip/constraints-on-archive

Add some constraint checking to archive
Move final_gift to Participant method

This is another of the scripts that are part of the current account
cancelation procedure, now moved to a (tested) method on the Participant
object. The script is still in place but now delegates to the method.
Merge pull request #2470 from gittip/final-gift

Move final_gift to Participant method