Remove e_data_book_view_register_gdbus_object().
Similar to EDataBook, the first thing we do after creating a new
EDataBookView is export its D-Bus interface. This was a separate and
failable operation. If the export fails, the EDataBookView is useless.
Perfect use case for GInitable.
Now we pass the GDBusConnection and object path directly to
e_data_book_view_new(), and if exporting fails the function sets a
GError and returns NULL.
This also introduces a couple accessor functions:
e_data_book_view_get_connection()
e_data_book_view_get_object_path()