…oaded pk3s when referenced by the server.

Ported from jk2mv.

Add ref_whitelist.txt, ref_blacklist.txt and ref_forcelist.txt.
Refactor reference handling to be more predictable (by making the reference conditions more explicit).

As many users don't review the content of pk3s when installing mods and as cl_allowDownload can download pk3s from the server the pk3 files in the gamne folder should not be considered trustworthy enough to run native libraries from. In case a user really needs it the unpacking of native libraries can be reenabled with a protected init cvar: com_unpackLibraries.

As the filesystem is initialized before the network socket the file descriptors
of the ip_socket turns out to be very high if many pk3s are loaded. When calling
NET_Sleep the select call is used to sleep unless something arrives on the
network socket. Due to its high number the highestfd value given to the select
call is very high and covers alls open files, leading to high load on some
systems. As a workaround this commit calls NET_Init before initializing the
filesystem.

…lds a handle for a file inside of a pk3.

…imum allowed file descriptors to 4096 on start (can be overriden with "-maxfds" on launch).

Ported from jk2mv.

If cl_downloadPrompt is enabled users have to confirm each pk3 download now.
If cl_downloadOverlay is enabled the window used for the confirmation prompt is used to display a progress bar and details on the current download.

…led by default and requires user confirmation.

Since com_unpackLibraries defaults to 0 the game is not going to unpack the default libraries from the assets anymore, thus the OpenJK ones should now be used as default.