Fixed a ton of two way radio bugs.

Added check for already linked radio
Added check for linking radio to itself
Slight output text change.
Added unlink checks.
Fixed radio not showing output values on mouse over.
Unlinking now unlinks both radios from each other. If a radio with an
existing connection is relinked.
Merge pull request #568 from DarkChowder/two-way-radio

Two-Way Radio: Fixed variety of bugs