Made Interactive Tooltip Header Configurable

Consuming code can now configure the header of the interactive tooltip. This has been configured for the engagement content view.

![screen shot 2014-09-30 at 8 05 05 pm](https://cloud.githubusercontent.com/assets/910510/4468655/9649bdbe-4901-11e4-9496-56f7149025ee.png)

@shnayder @dsjen @rocha