Accept asset/accessory improvements and fixes

[snipe]

We're seeing a handful of problems and inconsistencies with asset acceptance, so this is a whack at refactoring some of that.

Problem 1:

The storage/eula-pdfs directory did not have a .gitignore in it, which means it wasn't checked into the repo, so users trying to store the PDF would end up with errors, since the file couldn't be written to a non-existent directory. (We were also not checking to see the directory actually exists before trying to write to it.)

Problem 2:

We had added an extra column to the action_logs table called stored_eula_file, but that ended up being difficult to normalize in the API and the UI - and we already have a filename column on that table, so it makes more sense to just use that. (I'm still not entirely sure why we're duplicating the all of the data in the action_logs table in the checkout_acceptances table, but that's for another time.)

Normalizing this format means we go from something like this:

to something like this:

where the "uploads" and "acceptance pdfs" both show up in a unified way in the history tab.

Problem 3:

The stored_eula, the actual EULA text at the time of the acceptance, is being stored but not displayed anywhere. It will likely be long, and with the PDF support, I don't see any reason to try to cram it into the UI un the history tab.

I still need to do a little refactoring in the acceptance controller and clean that up a bit, but I think this isn't a bad start.

I also cleaned up the PDF layout a bit, so it looks like this now:

Still a few more tweaks to go, but I think it looks a little cleaner.

This will eventually hopefully fix #11116.