Remove redundancy from form/settings logic

[mjonuschat]

• Introduce settings object for all parameters
• Move calculated values into the settings object
• Subscribe the settings object to form changes
  • add a field to the settings object, mark the form input with data-settings to auto-update.
  • add automatic validation on all changes to the form for fields with data-settings marker.
  • automated updating of gcode preview by marking input fields with data-render
• Introduce a state object for gcode generation