todoist: move access_token to provider struct
This patch stores the Todoist Account access token in Provider structure. Since access_token is to be sent with every http post request, it is redundant to fetch it again and again. Hence this patch proposes to store it just once at the start. Also a function to emit access_token related errors has been added. https://bugzilla.gnome.org/show_bug.cgi?id=772278
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d811fede