detect: unify alert handling; fix bugs

detect: unify alert handling; fix bugs

Unify handling of signature matches between various rule types and
between noalert and regular rules.

"noalert" sigs are added to the alert queue initially, but removed
from it after handling their actions. This way all actions are applied
from a single place.

Make sure flow drop and pass are mutually exclusive.

The above addresses issue with pass and drops not getting applied
correctly in various cases.

Bug: #4663
Bug: #4670

(cherry picked from commit aa93984b7e58d3d8c1323f86bdaff937f8b8bd1e)