Add TCode Support

[flaretek]

Adds a mode in the startup menu for TCode.
When TCode mode is active, listens for commands on UDP 6969 and Serial.

TODO:

• Stepper doesn't move at a consistent velocity
• Make the speed control knob work to limit the max speed
• Consider additional safety features
• Packet buffering
• BLE?

Warning
Physical Safety Warning
TCode as a protocol is more similar to GCode. There is more potential for unexpected or erratic movement because motion is commanded based on position without specified acceleration. This branch passes the TCode expected position directly to the stepper library, which could result in rapid unexpected acceleration.
Commanding the machine with TCode could result in physical injury.
This code has not been tested for and is not recommended for any kind of penetrative use. This code should not be merged until additional physical safety controls are added to prevent erratic or unexpected movement commanded by TCode.
Do not test this branch unless you fully understand the above statement. Do not test this branch with the machine attached to a human.

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