Show function help popup in a dialog

Current function help shows a popup that overlays the function list, it wont disappear unless you click on the OK button (thus you can stack multiple popups if you click on various help links).

This commit changes the function help popup to a dialog, so if you touch outside the dialog it will disappear.

![2014-08-30 16 28 45](https://cloud.githubusercontent.com/assets/3890441/4099255/062bf528-3054-11e4-8269-fb155c7f7c4d.png)