Starting code to resize the graph dynamically

Initial steps towards rescaling the graph to better display detail.
Not completed.
Added code to dynamically rescale the graph

Tries to determine which sensors are active and keep those within the
bounds of the graph. For instance, if the bed is disconnected, zooms to
show only the extruder, allowing sub-degree changes to be shown.
Rescaling graph less frequently to reduce jitter

Should also run slightly faster
Fixing draw_temperature bug

Temperatures were being plotted upside down.
Increasing minimum zoom
Removing debugging statement
Merge branch 'resizing_graph' of https://github.com/sbliven/Printrun into experimental
Cleanup