Run Weboob as a daemon
Following the recent changes on Weboob interface to Kresus (see !430 (merged)) and related to #640 (closed), we should run Weboob as a kind of daemon. That is, spawn the Python subprocess when Kresus starts, and keep using the same process as Kresus is running.
This should also be simpler to do after #640 (closed) has been fixed.
Starting the whole Python stack and spawning a Weboob object takes a few seconds on a Raspberry Pi. That is a few seconds per API call. If we use a daemon-like subprocess, it would make the whole app a lot more fluid on such low power devices.