Enhance threadsafety of Hooks and improve generally

Enhance threadsafety of Hooks and improve generally

* bot:addhook may now be called from within a hook
  - hook mutex is recursive
  - It is unspecified whether a newly added hook will first run on the
    current or next hook match; depending on the properties of the
    hook either may occur
* Use general sorted list utilities instead of pushing to the back and
  doing a full sort on each add
* Incidentally replace String usage with std::string