Adding highlighting words

Off by default (no words added), the user can now use the /highlight commands to set any word to highlight the whole sentence, giving it an orange background.

In similar fashion to IRC, using /highlight add, yourname will make that every message with yourname in it will get highlighted.

You can add as much words as you want with /highlight add, word [, word]... delete them one by one in a similar fashion with /highlight delete, word [, word]..., delete them all with /highlight delete and show the current ones with /highlight show or list.