Adding type column and filter to assets list

@andy-armstrong - please take a look at this. (Sorry it took so long, other projects took precedence - as you can see I handed it off to @dino-cikatic midway).

This is the first time either of us has made changes to studio code, so hopefully we have everything we need in place for this.

(Also, we have one change from @frrrances herein for testing purposes - a necessary UI change otherwise the implementation looks to complex)
I forget the details here, but I'm surprised that the code would analyze the display name like this. In other parts of Studio the display name is an arbitrary human readable string. Is the display name always the asset file name? Could you maybe analyze the URL instead? In fact, it would be better to have the server return the asset type, rather than having the client guess it from the display name.