Update filter API to accept list of CustomEntityAttributes

see: https://confluence.unicon.net/confluence/pages/viewpage.action?spaceKey=ProServ&title=Implement+Additional+Campus+Extensibility+-+Extensible+Set+of+Name+and+Attributes

Once Custom Entity Attributes are defined in the admin interface, then the users can add them to a filter (where they will then be used to enhance the entity metadata).

• API to get the definitions : done/exists
• API needed to save the settings to the filter (as a modification to the existing save/create filter).

These get added to the EntityAttributeFilter - see: https://wiki.shibboleth.net/confluence/display/IDP30/EntityAttributesFilter