migrate away from bower

[noerw]

..its deprecated since a long time.

When sourcing dependencies from npm instead, adding a buildsystem becomes necessary.
I started this work already, but lost it due to my failed-upgrade-lost-backup-fuckup.
I used esbuild as a build system, as it's far easier to configure than webpack, and also much faster.

(Vendoring all frontend dependencies does not require a build system, and is probably easiest, considering that these dependencies don't need frequent updates)