rephrase spend limit and automatic deposit time interval

[williamstein]

The spend limit is computed based on the last 7 days (really 168 hours) from when you are looking at it.   It thus doesn't reset on a weekly basis, but instead, would only hit zero 168 hours after the most recent compute server usage.   I will change the wording and the button to make this clear, since by writing "Week" it suggests a calendar week.

It is at least easy to understand, define and compute the amount spent during the last 7 days.  It's very difficult to even define what a calendar week is, because it could start on Sunday or Monday, and is also a function of time zone.   Thus we're sticking with the rolling interval.

This ticket is about updating the wording/buttons for both:

• spend limits for compute servers, and
• automatic deposit configuration