Added "auto-height" option

The auto height option sets the extruded height for a specific polygon
based on its ID. If the polygon's ID is in either name_NNN_mm
or name_NNN_NNN_mm format, the NNN_(NNN_)mm part of the name
is translated into height in milimeters.

Otherwise, the height parameter is used

Examples:
  rect543_1_mm -> 1 mm height
  poly456_12_5_mm -> 12.05 mm height
  circle2345_3 -> according to the height parameter


Also, moved from tabs to spaces in the Python scrip ;)