Templates for captive portal proxy configration instructions

Templates for captive portal proxy configration instructions

Captive portals often have to bounce users to configuration instructions.
Those instructions consist of of how to setup WPAD or manual settings.
These templates allow for a standard and localized instruction set for
better support of mixed language users across any portal.

They are used by adding deny_info ERR_AGENT_... to the configuration.

The ERR_AGENT_CONFIGURE template utilizes visible_hostname and port info
from the responding proxy to display correct configuration details for
the gateway without requiring administrative re-write of the page.

Derived from work by the Mandrivia Project.

TODO:
 * some form of CSS agent detection to specialize the instructions.
 * add texts for other common agents