Added ajax throttling when tab is inactive.

* Added a window blur/focus listener to main.js, that sets the data property "isInactive" on the jquery window object to true/false. This property should checked using === as its initial state is undefined!

* Added a check if current window is active to the setTimeout of the updateTimes function.
Merge pull request #82 from verath/ajaxThrottle

Added ajax throttling when tab is inactive.