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

#394 changed the page title to "StrongLoop Studio Beta". I am wondering if this message should be kept in synch with that value?

Note that if we go down that route, then we need reference the string from `version.js` here, we must not copy the value. When Studio leaves beta, it must be enough to remove the "Beta" tag from `version.js` only.