Add env check for enabling mirrord explicitly via run configuration

[aviramha]

If user sets MIRRORD_ACTIVE=1 in their run configuration's environment, mirrord should run even if button is disabled.

[t4lz]

How about also accepting MIRRORD_ACTIVE=0 to disable mirrord for a run configuration even if the button is enabled?

[aviramha]

@t4lz I actually thought about it but felt like it's an over kill - they should just ignore the button and use the explicit for on always, not having means off for them.. but if user asks maybe I'll think about it again..