Support for printer gcode macros

There are certain things that printer owners need to do periodically to tune or maintain their printer. Many of these things require a series of GCode instructions to be sent to the printer. It would be nice to have a way to create buttons on the web or touch UI to execute locally stored macros that are not prints.

One example would be to move the print head to an accessible position, heat the head to a particular temperature and wait while the user replaces the nozzle on the printer to ensure a tight, leak-proof fit.

Or an easy filament change macro for users who don't have a display on their printers.