Make txt files from master server public over HTTP

[illwieckz]

Those 3 files are now public and retrievable using HTTP/HTTPS:

• https://master.unvanquished.net/ignore.txt
• https://master.unvanquished.net/featured.txt
• https://master.unvanquished.net/serverlist.txt

Sharing the first two makes easier to sync ignore list and feature list with secondary master servers.

Sharing the third one makes easier to implement third-party server lists. For example XQF can query master servers using either the good old Quake3 UDP protocol or by downloading such list through HTTP.

The two first ones are written by hand by the master server operator, the third one is automatically written by the master server itself.

We may do the same for motd.txt, but we have none for the moment.

The public.txt file is only used to map private IP addresses/subnets with public IP addresses so it doesn't make sense to share it neither to make it public.

Right now the master2.unvanquished.net secondary master server doesn't share those files over HTTP because there is no HTTP server for it yet.

[illwieckz]

The secondary master server now automatically syncs the featured and ignore lists from the primary one and rereads the files when a change happens.

That means adding servers to the featured or ignore lists of the master server would automatically propagate the changes to the secondary master server after a short time.