Make the limit mode of Motor input configurable

[rocco8773]

This PR does...

• Adds optional kwarg limit_mode to Motor. Default value is 1 to remain backwards compatible. This kwarg allows the class to be configurable for energized limits (1), de-energized limits (2), or not limits (3).
• Propagate the limit_mode setting up through the Axis and Drive classes so the setting gets properly passed through to Motor
• Update MotionGroupConfig to handle both required and optional metadata during every call to _handle_user_meta().
• Update TOML examples bapsf_motion.toml and benchtop_run.toml to include the limit_mode setting.
• Add slider widget to the DriveConfigOverlay (actually added to AxisConfigWidget to allow for setting of the limit mode.

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closes #86