refactor studio and composer into modules

/to: @anthonyettinger 
/cc: @bajtos 

- removed the app module
- split it up into studio and composer
- moved GlobalExceptionView to ComposerExceptionView

We already have a `profile` (see lines L144-149). When two identifiers differs in the last letter only (`profile` and `profiler`), it's a recipe for confusion.

Can you come up with more distinct names please? I don't mind renaming `profile` to something more specific too (e.g. `user-profile`).