PMAC: Implement motor jogging

Part of #2
Upon a command, we would like the PMAC device to jog one of its axes to a desired position. The command sent by EPICS to do this looks like `I122=2.5 I120=200.0 #1 J=100`, we would like PMAC simulation to respond correctly to this command. However, the separation of `#1` from `J=...` being dealt with correctly is dependent on #10, so for this issue it is sufficient to implement the correct logic such that `#1J=...` results in the correct behavior. The ivars will need to be set correctly, which requires #12.

## Acceptance Criteria
* Sending `#1J=X` will start the axis moving
* When the axis is moving we can get it's position through `#1P`, which is updated on each tickit update
* When the axis is moving we can see it's moving status using `#1?` (which is 0 when moving and 1 when done)