Add Vanilla Conquer C&C engine

[gizmo98]

Vanilla Conquer is a C&C engine which can run
Tiberian Dawn and Red Alert. https://github.com/TheAssemblyArmada/Vanilla-Conquer

[Exarkuniv]

@gizmo98
https://github.com/Exarkuniv/RetroPie-Extra already has it.
Not sure if it's something they would want to add since of how the file need to line up

[s1eve-mcdichae1]

WIP: https://gist.github.com/s1eve-mcdichae1/90edfe26d735a1b6e021ce523ee52e0f

I think this has improved file handling vs. the current RP-Extra module.

Installed executables are kept separate from user-provided game assets (or downloaded demo), and symlinks are used to combine them all in the install directory.

A unified launcher script allows for cleaner config dirs.

$home/.config/vanilla-conquer dir linked to $md_conf_root/vanillacc for network access and backup of savegames and configs.