Let force upgrade dialog be continued through in development builds

[nbrooke]

For the purposes of actually properly testing version deprecation, or checking something on an older build, it is occasionally useful to be able to skip the force upgrade dialog for developers or in-house testers.

We should add another flag like "isTestBuild" (maybe "isDevelopmentBuild", or maybe something more feature oriented like "allowDevelomentUpgradeSkipping"?) to the DefaultUpdateDisplay that will add a "continue" button even to the force upgrade warning, and probably change the warning to specifically mention that continuing is unsupported and may be dangerous.