Add login and signup flow

We can customize the SignupViewController to take in the additional
fields we need, right now it is just using the default PFUser object
and treating "username" as "email". When we get design assets for how
this should look, we can customize the fields. We don't need to use
the parse default SignupViewController, it should be really easy to
implement our own and use the delegate.
Add CRUD for Goal objects
Properly define the goal subclass
We don't need to explicitly cast Goal
Resolve #7: Add data model for Transaction
Resolve #9: Outline queries for transactions

- Use BFTask to make it easier to work with async parse methods
Resolve #10: Define query to fetch goals for a user
Resolve #19: Setup a basic view for creating a goal
Resolve #25: Create a simple view to create transactions
Issue #17: Create simple table view to display current user's goals
Issue #17: Create simple table view to list the current user's transactions
Merge pull request #26 from CodePath-MAF/feature-transaction-model

Merge a bunch of stuff