[Camera] Record mouse cursor

[thmsbfft]

https://twitter.com/grillitype/status/799307001671127041

Possible spec:
– Custom sprite for cursor or CSS code (color, border, etc.)
– :Active state (click animation)

[mylespalmer]

Both of those sound nice! Even if it's something more simple to begin with, like this — https://2.sendvid.com/s6osxv76.mp4 — that'd be a great step already.

[thmsbfft]

Added quick prototype code in 74a1a7e.

Some notes/next steps:
• The way Electron allows element to drag the window seems to mess with CSS cursors. Doesn't register the CSS above -webkit-app-region: drag, even if I disable it.
• I'm overriding the webpage's cursors by injecting CSS in them. So far so good, but it needs more testing + needs to work when navigating between pages (re-injecting the CSS).

I think I'll come back to this once video recording is no longer experimental (see #31).