Allow user to completely disable canvas content and related warning popup from a checkbox in TorButton's "Privacy Settings"

Canvas-based fingerprinting is a potent threat to anonymity. I believe it does not make sense to have it potentially enabled (following a popup dialog) at elevated Security Slider settings, and even with the Security Slider on "High," and probably also on Medium-High, Medium, and potentially Medium-Low.

Fingerprintable canvas content (and its related popup) should be completely disabled when the Security Slider is at one of these elevated settings, and it should be transparent to the user. It may make sense to still present the icon in the address bar so that it can be enabled manually, on a per-site or per-page basis, if a user needs this feature.

Thank you all so much.