Refactoring: change the application's architecture

I changed the client architecture so the model is (hopefully) cleaner and allow us to move forward the application faster (related issue is #95).

# New architecture

## General idea
* all files and folders are stored in one collection initialized in application.coffee
* when the user browse the app, a subcollection is created based on the folder it is browsing. For now, the subcollection is recreated each time but we can do so caching if we feel it's wrong
* the folder view is recreated every time the browsed folder changes (except for the search, to maintain the input state (see comment in related code)

Regarding "philosophy", I tried to make things simpler and more declarative so it's easier to maintain, but it can surely be improved.

## Model caching
One thing to note is that I added caching to folder. That means when you browse a folder the first time, its content is cached so when you come back to that folder it is displayed instantly. The cache refresh is ensured by 1°) realtime 2°) a request run every time the folder is displayed (in the background so the user can do his stuff in the meantime). So if realtime works, the user won't notice anything; otherwise it'll be able to benefit from fast display without being out of sync.

## Breadcrumb
I also fixed bugs (mostly in the breadcrumb). I simplified a lot the breadcrumb management, making it a part of the folder model and caching it. It might be over-simplified now because I dropped the Backbone.Collection in favor of a simple array.

## Upload
I moved code around in the various classes in charge of uploads. The upload itself is now performed by the UploadQueue collection, which represent the files to be uploaded. I think it will be fairly easy to display a merge version of the collection (based on browse folder) and UploadQueue to implement the inline uploader.

## File templates
I changed the file's templates (file.jade; file_edit.jade; file_search.jade) because they were unmaintainable as-is. It now uses jade inheritance so they are (very) smaller.

## Public area
I tried to make sure it works as before but I didn't make any of the planned changes because I assume this is not top priority and not part of the blocking code for the rest of the team.

## Quality
Needless to say that I have most likely introduced bugs that I haven't noticed yet; so even if I know you all want to see this merged ASAP so you can start working the app again, I'd suggest we all use my master on our Cozy this week-end to detect remaining and awkward bugs.

## Review
I let numerous `console.log` on purpose so people that will review the code can understand what's going on with caching and stuff. I also let a `setTimeout` on purpose in the server to actually realize caching works. Obviously I will remove them, rebase the code and force a push on my master.

There are also numerous comment with a `REFACTORING` prefix. Those are questions that I didn't want to answer alone or questions to myself that I forgot to answer ;-)

While I think reactivity is improved thanks to that, I also noticed that the application was **significantly** slower in terms of FPS on my MPB. No issue with my desktop which is faster by far. If you find any improvements (there are many, I believe) to prevent useless reflow etc. please let me know.

So please, don't merge before the PR is tagged "good to merge", thanks!
actually used in sharing modal