output-json: add app_proto key in root

output-json: add app_proto key in root

By adding the key in the root of *flow and fileinfo  events it
will be possible to get all events for one application layer by
using a 'event_type:proto OR app_proto:proto' filter. This will
permit to the analyst to get a good view of events related to
one protocol.

This patch also fixes a regression in file logging where app_proto
was available before 94dbd303e4744a40f3761265be7c73a7a4754764 create
the regression.