Swift templates

[walkingtowork]

@rmutter Still a lot of refactoring to do, but let me know what you think.

I feel like there should be a better way to write the parameters.py file, but I'm not sure how.

EDIT: Oh, I guess I broke like every test ever, so there's that too.

[rmutter]

@walkingtowork some first-round feedback!

[walkingtowork]

@rmutter Ready for some more feedback!

[walkingtowork]

@rmutter @baylee parameters.py needs better tests, and test_templates currently doesn't have any Swift templates, but everything else should be good.

[walkingtowork]

@rmutter Moved a bunch of stuff around and updated some tests, want to take a look?

[rmutter]

@walkingtowork here's some notes:

• I don't think we should have more than one TestCase per test_ file. There's a couple of times where you made a separate swift one, I think we may want to just better split the tests folder into sub folders that have iOS/ObjC/Swift test files with their respective TestCase.
• There's a few TODOs in the test files and the parameters file that I think are no longer relevant since you implemented the TODO.
• I'm not a fan of the objc_generator and swift_generator folders. I think they could just be called objc and swift? Also, their subfiles could just be called parameters, template, etc since they're under that specific folder.

[rmutter]

@walkingtowork :shipit: