api: new "pure" interface for plugins

Decouples the plugins from the core by not providing any implementation in the
interface. The plugins are expected to either implement the interface
themselves or use a help class for some of the work.
api: add new help classes for plugins

Implements part of the interface to make it easier to implement plugins.
icq: port to new api
jabber: port to new api
msn: port to new api
aosd: port to new api
auto-reply: port to new api
forwarder: port to new api
osd: port to new api
qt4-gui: port to new api
rms: port to new api
core: implement new api for handling plugins

Plugins implement one of the interfaces GeneralPluginInterface or
ProtocolPluginInterface depending on type. The instance implementing this is
separate from the instance of Licq::GeneralPlugin or Licq::ProtocolPlugin that
provides the interface to the plugin for other plugins.

Both Licq::GeneralPlugin and Licq::ProtocolPlugin are extended by
LicqDaemon::GeneralPlugin and LicqDaemon::ProtocolPlugin respectively to
provide an extended interface for internal use in plugin manager.

This provides a cleaner separation between plugins and the core.
api: remove old plugin api headers