Reset All Domain Shields on Global Toggle

[jhreis]

When a global shield setting changes (e.g. no_script), all no_script flags on Domain need to be reset to nil. This avoids accidental white/black lists.

Example:

• no_script is off globally
• user visits site X, and toggles no_script on, followed by turning it back off
• if user were to turn no_script on globally, the off value on website X would be overriding this

The other implementation option is to reset Domain shield specific settings whenever they are toggled to == global.

Example:

• no_script is off globally
• user visits site X, and toggles no_script on, followed by turning it back off
• instead of storing false for X.no_script, it is switched back to nil, since it is no longer performing an override.

This is probably more efficient.