Added a doc file with the organization of the code.
Improved text of usage.
Fixed wrong path to settings.
Added method to compute missing contracts in database.
Added new script to update cache.
Added viewport in HTML meta for mobile.
First implementation of celery.
Improved settings for celery.
Improved tasks for contracts and laws.
Added tasks for main.
Fixed paths of crawler's data.
Removed unused prints.
Added 3 log calls to contracts crawler.
Made info log call a debug log call in computing cached data.
Fixed error on contracts task.
Improved settings format.
Made celery scheduling to be every day at 4am.
Fixed task being called instead of added to a group.
Finished implementing job scheduling using celery.

This commit was tested both in staging and in production and
reproduces the previous behaviour.
Merged branch 'celery': implemented celery-based scheduling.

Made scheduling to be handled as tasks performed by celery instead
of pure Python scripts run by crontab.