[FIX] sale: force default values for dropped fields

Those values were dropped at rev 3b636a5 but
need to be forced back to default so older
databases get properly updated when upgrading.
[FIX] mrp: force default values for dropped fields

Those values were dropped at rev 9b34358 but
need to be forced to empty so older databases
get fixed when upgrading
[FIX] website_event_track: force type from related to fix bug with convert_to_cache on picture
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32