include steam and beginnings of arma3 and arma3-epoch server

todo: 

- [ ] test arma3 dockerfile
    - [ ] test assumptions about `wget steamcmd | tar`
    - [ ] configure arma3 to pull persistant data from non `/opt/*` paths
- [ ] create arma3-data dockerfile ?
- [ ] wait for arma3 epoch server files to be released and complete arma3 epoch dockerfile
needs to be tested, but essentially : 

- [ ] mods need to be pulled in from out of the image
- [ ] profiles need to be persisted and backed up
- [ ] `stdout` from `arma3server` needs to be piped somwhere useful (useful logger container?)