Draft: split totem-object

A split of totem-object so that we can have totem-window and totem-application.

Marked as draft because there is still some things to do:

• Find a way to fix totem_window_get_menu_section. Since we cannot access anymore to the menu id directly from the template.
• Fix warning in grilo when call gtk_application_set_accels_for_action since totem-object isn't a GtkApplication anymore.
• Fix warning about a g_hash_table_insert_internal: assertion 'hash_table != NULL' failed when clicking on the add button

I apologize in advance if the commits message are not good... 😅

Thanks

P.s: is there a way to update the docs automatically .... ?

Part of #547