Allow plugins to provide config files (for their dependencies)
A handler for 'couch_plugin' events'
Fire a log_request event when requests are logged
Merge remote-tracking branch 'asf/1867-feature-plugins-jhs' into 1867-feature-plugins

* asf/1867-feature-plugins-jhs:
  Fire a log_request event when requests are logged
  A handler for 'couch_plugin' events'
  Allow plugins to provide config files (for their dependencies)
unlink plugins from Futon & Fauxton