For the various commands, it is easier if we have a common interface
than just a simple function call.
Each current command runs something before the mainloop is created, and
then something after the mainloop is terminated. Having such a worker
allows us to have only one place where we start the mainloop, meaning
that the interactive prompt will not try to start it more than once,
and most above, will not kill it in the middle of a command while other
commands are still running.
Again, very rudimentary but we're planning on making kete a bit better anyway.
Also note that this doesn't make use of the tuhi.drawing module on purpose,
parsing the format twice avoids some bugs and also keeps tuhi-kete separate
from the tuhi daemon.
Part of #7
As we're planning to cache the data locally, the timestamps are a
unique-enough way that makes it possible to access a specific drawing.
And this way we can also delete some drawings without all other indices
shifting around.
Fixes#16
Benjamin Tissoires