Advanced DHCP Client Options & Config File Override

DHCP v4:
Protocol Timing
Send Options
Request Options
Require Options
Option Modifiers

DHCP v6:
Interface Statement
Identity Association Statement
Prefix Interface Statement
Authentication Statement
Keyinfo Statement

DHCP v4 & v6:
Config Override File
Add section tag to v6 documentation links.

Put v4 send, request, require & modifies in lease requirements and requests section.
No functional changes.
Config file formating:

FIX - Add new line after comment so first option statement is on uncommented line.
Prefix send host-name with tab.
Merge branch 'Advanced_DHCP_Client_Options' of https://github.com/N0YB/pfsense into N0YB-Advanced_DHCP_Client_Options

Conflicts:
	usr/local/www/interfaces.php