Add getGoal helper method
Add record payment function

Function to be used by staff members to record payment for a user. As this is running on cloud code space, we need to add useMasterKey() method to allow for the user object to be updated, hence being able to reduce their totalCash.
Add record cash out method

Function use by staff members to record cash out operations. It validates that a user can only be cashed out once per goal.
Merge pull request #10 from CodePath-MAF/staff-functions

Staff functions