Testing stream rules could not be applied to all message fields

The API was returning a filtered set of fields for messages retrieved.
Adding method to return filtered fields for other methods that rely on
it.
Keeping full set of fields in MessageResult and filtering fielfs in
accessor methods insteaf of constructor.
Adding new route to API that returns filtered set of fields, returning
full set of fields per default.

Fixes #528
add cache-control header for ajax

issue #540
use formatted value for field value searches

avoid using the display mapped value because that will not match the stored data anyway and often leads to syntax errors

fixes #539
Merge git://github.com/Graylog2/graylog2-web-interface into develop