This adds play/pause, restart, stop, next, and previous hotkeys to the
VLC source.

Closes jp9000/obs-studio#972

Allows having a bit more buffering for network-based video to prevent
things such as artifacting.

Closes jp9000/obs-studio#786

Adds the ability to add video playlists via libvlc instead of via the
media source.  This is mostly just being added as a secondary option to
the media source to reduce maintenance costs and save time.  Currently
libff cannot pause/unpause/seek, and isn't programmed to handle
playlists yet.

If VLC is installed on the computer (with the same architecture) it will
allow video playback via libVLC.  In the future, users should be able to
optionally download VLC libraries via the installer as well if they
don't want to necessarily install VLC to get the plugin working.

This plugin performs runtime linking instead of compile-time linking;
compiling VLC is not required, only its headers are required.  To
compile, clone the VLC repository and set the VLCPath cmake variable to
point to the VLC repository directory.