- Require all EPlugin and EPluginHook subtypes be registered before
  loading plugins.  This drastically simplifies the EPlugin/EPluginHook
  negotiation.

- Turn most EPluginHook subtypes into GTypeModules and register their
  types from an e_module_load() function (does not include shell hooks).

- Convert EPluginLib and the Mono and Python bindings to GTypeModules
  and register their types from an e_module_load() function, and kill
  EPluginTypeHook.