Spend down section should state month and year of the current eligibility period

[edmullen]

The Spend down section currently has the header "Current period". This should be changed to state what current eligibility period is, using the month and year. This will add clarity as to the specific time period.

[mgwalker]

This is going to need a change to the API /client schema. The "current period" should be reported by the API since the rest of the data is in the context of that value. We don't want to trust the client's browser to have the right time. This also mitigates timezone concerns, and has the accidental benefit of making it possible to report past/future spend down periods as well.