Expose getLevel(...) to LUA for command computers to query dimension info

[lexi-the-cute]

Useful information to include:

• Allows command computers to obtain their own dimension much like how they can obtain their own position via the commands api

I'm currently implementing a dimension broadcasting addon to my server's gps towers so computers can query their own dimension on top of getting their own positions. Currently I'm planning on implementing the dimension query API to behave like the GPS api, but with it running on rednet with the "gps_dimension" channel instead of using port 65534 like the regular GPS uses. I was researching how the command computers behave to more closely match the GPS api and discovered their is no way to obtain dimension information via the command api