Fix form usability issues

[nachtm]

This makes a number of small usability fixes to the form page.

We weren't validating that a species had been selected. Now, we are:

The loading overlay was stuck to the top of the screen -- now, it's not*:

Before, we weren't catching errors from report submissions, but now we're displaying an (admittedly not-that-helpful) message to users:

*This required a pretty big re-work of the drawer logic due to a bug in material UI. I'm happy to discuss/revert if we think the priorities are different. The solution I have is definitely hacky. But it addresses a couple of issues with the way it was structured before as well 🤷‍♂.

More specifically, material UI doesn't handle position: fixed well inside of drawers. In order to get the submitting indicator to follow the page, it needs to be position:fixed. I tried the workaround here, but it didn't do the trick. I also tried something similar to this, but regardless of the z-level I chose, I couldn't get anything to show up in the drawer. What worked was removing the drawer altogether. Then, I had to add a little more logic into Main.js to make sure that the header/footer didn't show up, and hooked in the open/close buttons. The only thing we've lost functionally is the swiping-up animation. Please try it out and let me know what you think!

This is a large change and I'd like your feedback -- I'm very open to ideas on how to do this with a smaller footprint

[sayas01]

Approved!!! 💯 Looks so much better!