Edit Budget tests and API-included Add Budget Tests

This adds one test case class for testing edit budget features, and adds two tests to the end of TestCaseAddBudgetActivity for testing responses from the server.

Both of which brings the coverage of AddBudget up from the red.

Also fixes a NullPointerException in AddBudgetActivity when in edit mode. The budget amount wasn't converted into a dollar-text amount, so it was trying to look up the amount by ID. I'm assuming the same thing happened in my edit entry pull request, but was fixed.

Additionally, this addition, tested without James' recent merge, brought coverage up to 56%.