updated rust edition to 2021 and rocket to 0.5.1

[archification]

Simply updating the project to be on current versions of Rust and Rocket.
As of rocket 0.5.0, the rocket_contrib crate was removed and rocket_dyn_templates is now used for templating.
We had to change the template filename from home.hbs to home.html.hbs because of an apparent difference in how this version of rocket handles filenames. I discovered this when I tried to launch the project but saw that the browser was rendering a file called "index" instead of "index.html". The maintainer of rocket responded in this thread stating that the file must be named with .html.hbs.