Add Objective-C file templates

These are intended to be rendered with ERB
Use erb for template names
Add directory structure to liftoffrc
Initial stab at ProjectBuilder
Remove main storyboard from info.plist
Link files properly

Uh...holy shit. This works now.
Create unit test bundles
Extract Project
Wrap target groups in a directory

We don't need to be doing anything tricky here. If people don't want
these groups wrapped in a top-level group, that's their prerogative.
Move gitkeep stuff to FileManager
Reorder groups before saving

It was driving me crazy to have `Products` and `Frameworks` showing up
above our groups. Fixed now.
Small improvements
Use default values from liftoffrc

If the user has specified name, company, author, or prefix settings in
their liftoffrc, we should default to those options, but allow users to
override them.
Move project directory creation to file manager
Force prefixes to be uppercase
Run original liftoff commands on generated project

This is actually breaking backwards compatibility right now. With these
changes, users will not be able to run liftoff on existing projects.
I'll fix that in another commit.
Move reading template contents to file manager
Save the project directly

We don't need to save the project in any crazy way, so we might as well
inline this. It will also force me to refactor this out soon since it's
annoying.
Remove unused project file helper

We are passing in the name of the project file, so this is unused now.
Configure default code signing entitlements

This is needed for building for a device.