Better index page

This is somewhat in line with henry's designs but I haven't strayed too
far from what the admin template styles do by default
There are also some decisions to be made about whether this is ever seen
after sign in and some Jinja logic to fill in
Add data set list and upload form partial

Jinja logic needs filling in
Again, inline with designs, not close to pixel perfect
Upload error template

does not include table
Upload okay partial for use with the data sets list
Add in jinja logic