Simple multi pen support with pause/resume.

[techninja]

Issue 242: Super simple pen support

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This pull request does the following:

• Adds general simplified support for using multiple drawing implements via manual swap.

Setup for review:

• Pull this branch and run RoboPaint from code via npm start

To Review:

• Open up settings, and select No water/paint pen pencil mode
• Select Pen/Pencil generic multi from the colorset dropdown
• Pick an image with multiple colors in print mode, and click print
• See that you're prompted for each color, can calibrate each pen, and continue through to complete the print

[techninja]

Will remove the "Work in progress" note in title and fill out review steps when I have this fully working.

[techninja]

TODO:

• Builds are failing for cncserver, which needs to be merged and published before this can get merged (It's Serialport that's to blame!)
• Pen/Pencil colorsets should be all that shows in the dropdown when selected.
• Single Pen mode seems to be broken.

[techninja]

Good:

• Builds fixed for cncserver!
• Fixed the bug I saw with single pen mode
• Added keyboard shortcuts to the workflow, works great!
• This totally works great for relatively small straightforward prints.

Really bad:

• Large command renders appear to need to be completely sent to be able to get ANY height command in for initial calibration. Either need to have calibration BEFORE the rest of everything sends, or figure out a way around this.
• Screen position vs bot position seems WAY off, and on the mandala test, the first pen color didn't switch before it started drawing the other color. These may be related, or not. Need an easier test case to debug.

This is just not quite ready :P