Make credit card charging patterns more predictable

[ChimeraCoder]

This comes via @chrishwiggins - the amount that will get charged to my card (or how often my card will be charged) is a function of both

1. How much I am giving to others on Gittip
2. How much other Gittip users are giving me
3. How much money I already have in my account

These aren't hard to calculate, strictly speaking, but it might be nice to present this to the user, to make the charging patterns more predictable.

Chris compared it to Uber, where it's hard to know how much you'll pay until the ride is complete - not sure how illustrative that analogy is, but I can kind of see the point he's making.

[chadwhitacre]

+1

[chadwhitacre]

This could overlap with #1063. It's about making our rather complex funding flows as visible as possible.

[chadwhitacre]

Closing in favor of #1063, with comments copied over there.