e_policy_wl: add new funtion for tizen_ws_shell extension

e_policy_wl: add new funtion for tizen_ws_shell extension

For make extension protocol for tzsh in seperate module, added the two functions.
1) e_tizen_extension_add : this funtion should be called in module_init
2) e_tizen_extension_del : this funtion should be called in module_deinit
When received tizen_ws_shell::get_extension, server call the callback to create
specific resource for extension. In callback function, it should be make new wl_resource.

Change-Id: If34fa96ee3460ca8df20c6fddb66bccd2b845006