Feature/3944 add file browser to projects#show

[euler-room]

This PR is incomplete:

• - needs tests
• - sorting is functional but buggy
• - code could be better organized

[johrstrom]

This is so big it's going to take me a bit to go through.

At a glance though, I did not expect so many updates to the project models. It seemed to me like this is would initiate on the client side.

I mean I'd envisioned it as on initial load, there's some empty div, then there's client side javascript to make a query to the files controller that then returns the partial. So that the project controller doesn't even really know/care about any of this.