stop allowing unbacked tips

[chadwhitacre]

Surfaced on #95, due to the complication this adds to queries where we want to aggregate tips. Right now you get a highlighted "Back your tip with a credit card!" link inline when you try to tip unbacked, but the tip is still recorded in the db. The idea would be that when you try to use that part of the UI, redirect to the add a credit card without recording the tip at all. The downside would be that the user wouldn't have those tips waiting for them on their profile page to remind them who they wanted to tip.

[thiloplanz]

How does this relate to purely pre-paid gittip accounts? Many people do not want to allow automatic charges against their credit cards, but would still participate by pre-paying.

Is it possible that a tip can remain "backed" by a pre-paid deposit even without a card linked to it? (It would stop being backed when the deposit runs out).

[chadwhitacre]

@thiloplanz Reticketed pre-paid accounts as #113.

[chadwhitacre]

I think the somewhat more complicated queries are the right answer to this. Better to record more information than less.