Initial addition of settings and temperature control to Panel
made some fields private in stepper steppermotor stepticker
Added e steps for panel
fix minor update bug after changing a value
add z homing offset to settings
Enumerate hotends for display in panel temperature settings
refactor the panel to be a singleton saving having to store panel pointer in every screen
lazy load the configure screen
Merge pull request #407 from wolfmanjm/panel/add-settings-and-temp

add settings and temp to panel, refactor panel, minor refactor StepTicker