Clean up schematas

Hide and protect (ManagePortal) unused fields.

General suggestion:

``` python
HIDE = [
    'location', 'language',  # Categorization
    'creators', 'contributors', 'rights',  # Contributors
    'allowDiscussion', # Settings
    'nextPreviousEnabled', ]
```

Depends on type:
'subject', 'relatedItems', # Categorization
'effectiveDate', 'expirationDate',  # Dates
