Simplify EPlugin loading at startup.

- 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.

modules/plugin-python/example/hello_python.py

@@ -0,0 +1,5 @@
+'''hello_python.py - Python source designed to '''
+'''demonstrate the use of python Eplugins'''
+
+def say_hello():
+    print 'Hello ! From python'