* Adds ability for self hosted custom menus
Templates can be added to /etc/netbootxyz/custom and are
generated and placed in the custom directory of the root
web directory by setting custom_generate_menus to true.
This provides an option on the main netboot.xyz menu to chain
into a custom environment so that seperate local menus can be
added and maintained seperately from the netboot.xyz source
code tree.
* Remove todo