Use RubyMotion's default project file

Hey Clay,

RubyMotion's file list has a default file list of `app/**/*.rb`. This change removes the need to specify which files are scanned and just uses RubyMotion's defaults if no files are explicitly passed.

With this change, the following two invocations do the same:

```ruby
Motion::Require.all(Dir.glob('app/**/*.rb'))
Motion::Require.all
```