Add seen and tell functionality

[datr]

See:

https://github.com/wiredfool/jibot-tng/blob/master/scripts/seen.coffee
https://github.com/wiredfool/jibot-tng/blob/master/scripts/tell.coffee

Consider also trying to implement Github's script to search the network for known macaddresses. This might be difficult because of the small subnets we use on the ADC. If the IPs are static enough we might be able to search for that instead though.

[datr]

Tell already exists in hubot scripts: https://github.com/github/hubot-scripts/blob/master/src/scripts/tell.coffee