[rfc] Optional Disabling of Detection

For people who what to use Suricata only for logging of events (http requests and such), this patch set introduces options to disable the detection module.

It modifies startup, runmodes and transaction handling.

Prscript:
- PR build: https://buildbot.suricata-ids.org/builders/inliniac/builds/130
- PR pcaps: https://buildbot.suricata-ids.org/builders/inliniac-pcap/builds/50