Update readme, change %participant_id to %username
Merge pull request #895 from buttscicles/readme-update

Update readme, change %participant_id to %username
Fix #898

The first_time_tipper key is used to drive Mixpanel metrics on the
client side. Apparently we have someone POSTing to tip.json without an
amount in the body. I'm pretty sure we want to let that happen (we do
have a CSRF safety belt).
Bump version to 8.0.19
Bump version to 8.0.19-dev
Add a target for makeing a cloud db; #415

This hits api.postgression.com and writes the result to DATABASE_URL in
local.env. There is no error checking (last week postgression was giving
me a "none available" error message for a while). Also, postgression
instances only live for 30 minutes, which isn't great for the dev use
case.
Simplify README around dev db setup; #415
Implement a receipt for credit card charges; #83

This is a simple receipt for a single credit card charge, keyed by the
exchange id in our table of that name. It is only available to admins
and the participant in question.
Bump version to 8.0.20
Bump version to 8.0.20-dev
Fix key for card_type in receipt; #83
Bump version to 8.0.21
Bump version to 8.0.21-dev
Return 404 for bad exchange id; #83
Bump version to 8.0.22
Bump version to 8.0.22-dev
Rough it in! Here's community pages. #496
Bump version to 8.1.0
Bump version to 8.1.0-dev
Fix regression with tipping; #906

I added chosen for the community chooser UI. I was only serving the
js/css assets on the profile-edit page but the profile.js that loads
apparently elsewhere was not seeing them and causing tipping to break.
Eep!