[FIX] mrp: force empty values for fields that were dropped

This ensures the field values are cleared during
upgrades from previous versions
[FIX] product,purchase,point_of_sale: force empty values for dropped fields

At 96f038a product-related fields were removed due
to an important product.template/product.product
refactoring. As the field values were simply
dropped, they may not be nullified when upgrading an
existing database. Forcing them to False will take
care of it.
[FIX] hr_recruitment: fixed computation and storage of day_open and day_close + assignment of date_open and date_closed.
[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
[FIX] website_blog: wait that document is ready before to check if we need to update menu for blog
[FIX] website_blog: change group restriction to load the JS editor
[FIX] website_blog: fix js error from 0a8aad990c86b18dfba5bb5dc964847fd97e7153
[IMP] point_of_sale: field company_id on pos.config view

Move invisible field on bottom to avoid blank space in view if display journal, group or sequence field
[FIX] models: in onchange(), do not send a field value if it has not changed

The method onchange() executes onchange methods in cascade.  Suppose onchange()
is called and a field F=1 in the form.  If an onchange method set F=2, that
value is put in the result variable.  If another onchange method set it back to
F=1, the binding F=2 must be removed from the result variable.

Fixes #2309