Rename GTasks Task list

[marbetschar]

This PR fixes #163

[danirabbit]

This works as expected for renaming GTasks lists. I am encountering this error though:

(io.elementary.tasks:5319): GLib-GObject-WARNING **: 11:34:30.995: invalid cast from 'EGDataOAuth2Authorizer' to 'GDataOAuth2Authorizer'

[marbetschar]

@danrabbit that's probably due to the following line in the code:

var oauth2_authorizer = (GData.OAuth2Authorizer) new E.GDataOAuth2Authorizer (collection_source, typeof (GData.TasksService));

tbh I don't know if that's the way how the code is intended to be used. As there is no unified, high level API for task list managing in libedataserver I'm doing a lot of guess work here. But I don't see why libedataserver should provide a E.GDataOAuth2Authorizer other than allow for authorization to use a libgdata backend - therefore casting it to a GData.OAuth2Authorizer seemed like the way to go.

[marbetschar]

maybe @tintou knows, if this the correct way to glue libgdata and libedataserver-1.2 together?

The below code produces a warning (invalid cast from 'EGDataOAuth2Authorizer' to 'GDataOAuth2Authorizer'), but other than that it works:

var oauth2_authorizer = (GData.OAuth2Authorizer) new E.GDataOAuth2Authorizer (collection_source, typeof (GData.TasksService));

[tintou]

@marbetschar I've now opened https://gitlab.gnome.org/GNOME/evolution-data-server/-/merge_requests/57
Just FYI, after this PR, the .vapi contains this:

public class GDataOAuth2Authorizer : GLib.Object, GData.Authorizer {

So you might want to cast to GData.Authorizer instead.

[danirabbit]

Works as expected. No more Terminal errors. Nice job :)