Override Compatibility Mode in Internet Explorer

The X-UA-Compatible meta tag should be added in the head of Apigility
Admin pages to avoid IE rendering the page in Compatibility Mode.

Below is a screenshot how Apigility Admin UI looks in IE Compatibilty Mode:
![ie_compatibility_mode](https://f.cloud.github.com/assets/468091/2435919/fad03d74-add1-11e3-937c-2d81551010af.png)