Let's ask people to support us
Polish up styles on "support Gittip" message
Tweak words and colors
Factor out Gittip.tips.set

I want to set a tip from somewhere besides the existing tip widget.
Switch how we update the tip widget

Without this we were getting 0.5 instead of 0.50 in the tip box after
changing the tip.
Wire up tip buttons in global CTA
Make CTA dynamic

Varies based on current percentage of backers:

 - Less than 30% we appeal to pity and goal: "Only 5%! 20%?"
 - Less than 70% we appeal to goal: "48%! 60%?"
 - Above 70% we appeal to herd: "80%! Join them!"
Tweak colors on buttons

Draw primary attention to the low number
Implement "No thanks" and conditional display

I went with a `rides_free` column on the participants table, with
default of NULL, that is set to TRUE when a user tips us and FALSE when
they explicitly opt out by clicking "No thank." This field isn't used in
the calculation of the percentage of supporters among active users; we
still use the actual transfers from last payday for that. This field is
just used in deciding to display the message to the user.
Pester everyone; 10¢ on the low end
small refactor
don't recompute the number of backers
Rationalize payment suggestions
Write a Pricing page
Tweak styling and verbiage
compute usage only once
Tweak styles/verbiage and wire up payment button
Fix little bug in pricing button
Actually, we don't use H1 this way
Lay groundwork for homepage + responsive

Moves "support Gittip" banner to a template and redo the markup to be
variably stylable.