Version 2.5.0 - Post-processing redesign

Learning more about Python and gcode made me rethink how I was implementing post-processing in my plugin.

Most of the important changes are under the hood, however, in this version:

• Post-processing is now based on print height rather than layer number, which means that towers are a bit more accurate
• Preset towers are now designed for, and will work best for, the most common layer heights that I use (0.10, 0.12, 0.20, 0.24, 0.30)
• I've reverted to using the M220 feedrate percentage command to adjust the speed for print speed towers. This is not entirely accurate but may be the best method for now
• The comments in the gcode is more standardized and useful, so people can point out where I've made mistakes easier!
• The plugin will adjust some print settings that are critical to the tower being printed, but will no longer remove the tower if you change those settings
• A few more miscellaneous changes
• I've tried to thoroughly test this, but there are almost definitely plenty of new errors to find