Custom fomantic-ui build

[silverwind]

As mentioned in #9374 (comment), the version of fomantic-ui we use is very big and includes around 30 modules of which we probably only use a handful, so I'd estimate we could drop the size of it by at least half if not more.

Proposing to add a custom build process that adds it as a npm dependency and a make fomantic-ui target to build it.

As a first step, we can commit the resulting files in the vendor directory, but I'd like to eventually have them integrated in the webpack bundle, but that could prove a bit challenging as it needs the right webpack loaders for the fonts etc.

[silverwind]

Fixed with #9561