This is a more robust implementation, where tasks are properly
stored (hey, I came up with a super cool stacking algorithm to
get that right!) and properly escapes the strings before sending
them through POST requests.

This also reorganizes the code, adds a much valued debugging and
tracing spews, and takes error management to a new level with
proper error reporting, GQuarks and stuff.

And to put the cherry at the top of this reimplementation cake,
this make the code a little bit less redundant in many places.

A few things to do still:

 * Figure out how to implement comments and attachments to tasks.
   This is a premium feature of Todoist.
 * Stop using Online Accounts. It is already condemneded to doom.
 * Properly report errors to users. This is coming up later.