[FIX] read() method returns None values incompatible with XML-RPC
Merge pull request #1284 from sebalix/8.0-fix-xmlrpc-marshall-none

[FIX] read() method returns None values instead of False, incompatible with XML-RPC
[IMP] improve graph view layout and groupbys

* add a 'total' foldable button to allow the user to control the column
in pivot table view
* in the dropdown menu, add all fields from the model instead of only
those from the search view groupbys
[FIX] correctly type date field in crm_lead_report

opening_date and date_closed were cast to char but are supposed to be
dates.  When you try to group crm_lead_report by one of them, postgres
was not happy.  Now, it properly tells postgres that they are of type
date.
[FIX] correct various date issues in reporting

* remove old 'day', 'month', 'field' and replace them by the actual
date/datetime field
* remove weird cast to char when creating the view to prevent crash
when grouping on them
* remove duplicates (such as 'creation_date' and 'create_date')
* fix typing errors (field type date defined as a datetime in the
postgres view)
* fix search view definition
[FIX] addon web: prefix css dropdown-submenu

to prevent possible future conflicts
[IMP] sale, crm: remove remaining interval filters, continuing 366a30d
[FIX] loading modules: load custom models earlier so that they are available when setting up models