Allow for easier file loader integration

[ivmartel]

The file/url loading code is not flexible: it is complicated to add support for a new file extension. This must be made more adaptable.

[rafasoyyo]

The ability to load arraybuffer directly and stop loading will be appreciated, especially in urls.

[ivmartel]

Ok... What would be your use case?

[ivmartel]

Have you seen what @tmskmr did in #332? His memory class is what you are asking for?

[rafasoyyo]

Yes, this is usefull te load data from Arraybuffers.
A generic method like app.stopLoading() to be able to cancel load progess can be also usefull.

It is just an idea...

[ivmartel]

I create a specific issue for stopping the load: see #340.