[DNM] Terminals.

WIP for a new unified computer system type. 

- [ ] Add construction steps for basic terminals.
- [ ] Work out how to handle networking, wifi range, and subnets.
- [ ] Implement user accounts and sessions.
- [ ] Implement file permissions.
- [ ] Implement flash memory/external devices.
- [ ] Implement a bash scripting expy for basic automation.
- [ ] Properly implement abstract data types (text, image, binary).
- [ ] Implement file encryption.
- [ ] Implement daemons.
- [ ] Implement both graphical and command line interfaces for programs.
- [ ] Convert existing 'programs' (console functions) to /datum/computer_file/program.
- [ ] Bugtest bugtest bugtest.