Client changes from prototype

[vteague]

This merges the prototype client UI into the updated branch of colorado-rla. Also added a button for getting assertions as CSV.

Note this is not intended as production code - it's a no-frills interface with basic functionality.

[charliecarlton]

Changes look good although I noticed a couple of things that could be (but probably not) related.

1. When I estimate sample sizes on this branch it fails and I get this error:
   INFO MatcherFilter:162 - The requested route [/estimate-sample-sizes] has not been mapped in Spark for Accept: [text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,/;q=0.8,application/signed-exchange;v=b3;q=0.7]

2. Definitely unrelated to this case but noticed while testing: When I Reset the database to start a new audit, the assertions tables do not get emptied. Not sure if that's been an issue for you all or if you have a different way of getting everything set up for a new audit.

[vteague]

Thanks for your reviews @charliecarlton

1. Estimate-sample-sizes isn't currently expected to work - that endpoint is still on the todo list.
2. Good catch re ensuring assertion tables are deleted when resetting the database - I've added a card at Ensure assertion tables are deleted when database is reset #149