Users mentioning/tagging

I'm pretty sure it's broken and I'm pretty sure it's ugly.
The only good thing is that it **should** work. (Not tested much, so it may even be broken :innocent: )

It inevitably adds some load on the server when posting (it has to run some weird code, load quite a bit of data and execute a pretty heavy query, but hopefully that one is cached, so it should not be such a pain).

Doing it in javascript in a sort of autosuggest would have a much smaller impact, though I'm not a javascript guru... lol