Canvas support has a couple of bugs

[PaperOrb]

I excitedly tried the new update that added canvas support (see issue #34) and noticed two bugs:

1. After opening a few canvases with several notes each, virtual content stops displaying for subsequent canvas file notes (hard to pin down an exact amount, but it doesn't take much).
2. Displaying virtual content in the sidebar or in a separate tab for notes in a canvas isn't possible.

[Signynt]

Canvas support is really hacked together, and has a bunch of small issues and bugs. I've tried to get it working as smooth as I can, and will take another look at it in the future, to see if I can improve things. It's pretty opaque to trouble shoot, which makes things harder.
Thanks for reporting these two issues.