Disable network/fpp settings page content so we can merge 'dev' to 'master'

It was brought to my attention that my changes were holding up progress
on other work so I figured we could print "coming soon" messages on the
work-in-progress pages for now.  This will allow us to merge to master
for people to have some updates.

This will now make it such that people have the argument parsing,
settings changeable, more linux-y FPPD as well as the changes to
enable/disable password protection of the web UI and timezone
configuration.
Let the user know that the username will be "admin" when setting a password
Fix bug with old config files exposing a crash.

Pointers for key and value weren't set to 0 because I thought they were
always being used.

When we hit the last else in processing the key, we never set value.

After the big loop checking the keys we cleanup any allocated character
arrays and since value wasn't set to null at instantiation we tried to
free it, causing a segfault.
Reintroduce SUDO as a define.

I previously removed some sudo calls that are required for things to run
properly on the PI right now.  As an easy way to toggle installations I
added SUDO as a define that can be set as "sudo" for something running
sudo (like the PI) and the empty string for a linux based install where
things are configured to run as www-data or some other user.

Eventually I'd like this to be either auto-detected or a configurable
option.
Update fppxml.php to write out volume and mode in new settings format.
Fix minor problem in SetFPPDmode function