Prune OLD_AMOUNTS, per old comment; #1041
Set new tip amounts, 100 down to 0; #1041

I'm going to change from buttons to a select dropdown for tip amounts,
with these options.
Change tip buttons to select dropdown; #1041

Still need to wire up in javascript
Wire up new dropdowns for tip amounts; #1041

I largely de-duplicated the tip UI amongst /on/elsewhere, participants
on Gittip, and the Giving page under the profile. The group tips for
GitHub orgs ~= Bitbucket teams is still WET.
Bump version to 9.1.0
Bump version to 9.1.0-dev