Combine JS/CSS & massively simplify build

- All JS and CSS are boshed into combined.js/css [Delivers #75439298]
- Move all of build.sh into Makefile as this is what it was born to do.
- Use intermediate directory `./build` and output directory `./public`
 instead of `./compiled`
- Symlink rather than copy `fonts` etc
- Only make single .tar.gz file pilotplanner-latest.tar.gz
- Allow `watch make` to simplify development [Delivers #84475818]