#1225322 by pcambra: Allow to submit/validate form elements placed in area handlers (header, footer, empty)

Add uses_exposed_form_in_block() method to the display so that CTools can specifically make content panes have exposed form in a block.

#1207680 by damz: Don't validate if there are no options set, the values are empty and required is not set

This reverts commit 2559eea4.

This reverts commit e1adbdc2.

Issue #1207680 by dereine: Don't validate on term filters, because this causes views to not to save anymore. Added TODO

If you have added a field before a language you have LANGUAGE_NONE as field key,
but you current site language is for example 'en'. So add LANGUAGE_NONE as possible value for a field.