New Release Candidate - V0.3.3rc2

Is anyone out there willing to upgrade OctoPrint and Octolapse in the name of science? You can install this latest release candidate from within the plugin manager using this url: https://github.com/FormerLurker/Octolapse/archive/v0.3.3rc2.zip 

**This version supports only OctoPrint v1.3.9 RC3 and above! Please double check your OctoPrint version and upgrade if necessary BEFORE attempting to install this release**

Please post any problems you encounter to this github issue: https://github.com/FormerLurker/Octolapse/issues/198 

You might be thinking, "Didn't we skip a few versions?" And you'd be correct. The TL;DR of the matter is that I've been having difficulty keeping my versions straight (still new at this). Some changes in this version should help me with that.

There are lots of new exciting features in this release candidate:

Enhancements:

• This release candidate supports maintenance and development channels within the software update plugin. Now you will receive update notification based for release candidate and development channels depending on your settings! Commit tracking does not yet work, but may in a future release.

• The 'Position State Info Panel' on the Octolapse tab has been simplified and enhanced to show . The icons have been cleaned up. Any states that could prevent your timelapse from working now show up in red. Additionally, the slider on the Octolapse tab under 'Current Settings' will now display in red if there are problems. Note that these items within the info panel (XYZ Homed, Extruder/XYZ mode, Metric Units) will be in red at the start of a print, until the proper gcodes are detected. 

• Thanks to a helpful contributor (shadowen), Octolapse now supports GIF output and custom watermarking!  Unfortunately GIF video will not synchronize with the default timelapse plugin at the moment, and must be downloaded manually. This will be fixed in an upcoming release of OctoPrint.

• Octolapse now supports custom GCode scripts within OctoPrint (Settings->Printer->GCODE scripts). Previously this caused some major problems for people.  Now it will process just like any other GCode! 

• Octolapse supports a brand new OctoPrint hook that will allow video synchronization with the default timelapse plugin for all supported file types. This won't be available until a future version of OctoPrint, but Octolapse will support it as soon as it is released!
• Octolapse now has basic support for firmware retract and detract. This feature is in its infancy, however, and needs some thorough testing.
• G2/G3 Arc Move is now supported within the position tracker, though not for position restriction intersection calculation (boy that was a mouthful!). It is very difficult for me to test this currently, because I don't have a slicer that can utilize G2/G3. If someone can supply a test GCode file for a Prusa Mk2S, I'd be very appreciative! 

Bug Fixes

• Snapshot are now stabilized properly when extruding in absolute mode if G92 commands are sent while a snapshot position request is active. This should solve the 'jittery' timelapse issues that have been reported by some when using absolute extrusion.
• Fix problems some end-of-print and cancelling that caused some deadlocks in some cases. This fix is why 1.3.9rc3 is require for this release
• Fixed print start detection problem for Octoprint 1.3.9rc1+. Basically Octolapse would never start in these versions of Octoprint.
• Fix GIF rendering issues.
• Added new version requirements. Octolapse now only supports OctoPrint v1.3.9 and above.
• Fix some JavaScript errors.