Run multiple MPF-MC instances

[qcapen]

The intent has always been to allow MPF to run multiple instances of the MC simultaneously. However, there are currently several issues that prevent this from working:

1. Config players use a hard-coded BCP connection name (each MC instance will have a unique connection name). This is already an MPF issue: BCP connection name hard-coded in plugin players mpf#943

2. There is no way to designate assets for a specific MC (unless it is running on a separate machine). This means the asset loader will use the same paths for each instance and there will be duplicate assets in all MC instances. It would be nice to configure asset paths for each MC instance.

3. I'm sure there are other issues related to multiple MC instances so when they are discovered, please place them here and edit this issue.