Make lobby page great

[ajuvercr]

The lobby page is one of the ugliest pages in Planetwars, please fix.
This page loads dynamically the state and put's that HTML code in a div, ugly ugly.

Resources: backend/src/util.rs:13 for the fields in GameState.

The useful files are probably backend/templates/{lobby, state_partial}.html.tera, backend/static/script/lobby.js and backend/static/style/style.css.

Optionally: move lobby css to its own file.
Optionally: find different way to refresh the state, now it just reloads its state part.

[ajuvercr]

It's already a lot better, still could use some improvements though!