disolving wookie-plugin package, merging into wookie.

the purpose for this is that all the plugin functions are core. i
originally created wookie-plugin to shield the wookie namespace from
plugin-defined functions before i had a clear idea of how the plugin
system would work. now that plugins are isolated as their own
systems/packages, there's no need for wookie-plugin anymore as it's just
another core piece of wookie.

also converted set-plugin-request-data/get-plugin-request-data to
plugin-request-data (setfable function). much cleaner interface...