Display alert when page zoom is not 100%

@kadst43 @eric79 

This detects the browser zoom level and alerts the user as well as instructs them on how to fix it. If the zoom level is not 100% at startup, then a reload is required to fix it. Otherwise, the alert will disappear when the page zoom is set to 100%. The alert also scales inversely with the page zoom so that the size on screen remains constant (no, this can't easily be done to negate page zoom in general). This works in Chrome, at least on my machine, so give it a test to be sure. I haven't tested other browsers.