Changes in UserProvisionable Table (no longer keeps control of contract/offers) and making the logic of find charges exclusive to the accounting module. Added management command that finds all the open provisioned items for a period and creates charges for them.

Signed-off-by: Raphael Lullis <raphael@lullis.net>
Merge branch 'master' of ssh://github.com/litedesk/litedesk-webserver-provision