Add new System Hardening menu and options to bsdinstall.

This patch add new 'hardening' file responsible for new bsdinstall
'System Hardening' menu allowing users to set some sane and carefully
picked system security options (like random process id's, hiding
other users/groups processes and others).

All options are OFF by default in this patch due to POLA principle
with intention to turn change some of them to ON by default in future.

Reviewed by: adrian, allanjude, bdrewery, nwhitehorn
Approved by: adrian, allanjude
MFC after: 7 days