Since packr have been deprecated in favor of go:embed for quite some
time now I have replaced it with plain go:embed functionality which
makes it more future proof.
The only downside is that go:embed can use relativ paths only, that's
why I have moved the web/dist folder into api/public.
Besides that I have refactored the static asset handling which includes
basic last modification and cache control headers to improve the cache
cache behavior for static assets.
I have updated all dependencies within go.mod by executing `go get -u
./...`, beside that I had to replace the imports for logrus, mergo and
squirrel to match the right names from their modules.
