Move remainder of Angular app under frontend

Templates, project infrastructure, configuration.

See 6ec5ca58, #2261.

Also handles:
https://community.openproject.org/work_packages/17538

Continuation of code reorganisation started in #2193. This PR will another step towards allowing us  to move the frontend app into a separate repo.
@0xF013 it is indeed. In fact, we can probably safely remove `jquery_noconflict`. Webpack only exposes `jQuery` as a global.