v0.1.6 be able to have mkt-prompt part of the page, html5 validation

Should this be renamed to mkt-form? 

**\<mkt-prompt\>**

![screen shot 2014-12-22 at 11 24 59 am](https://cloud.githubusercontent.com/assets/674727/5529794/2f4ce3a4-89cd-11e4-9a4a-318ae27d3fc4.png)

**\<mkt-prompt data-modal\>**

![screen shot 2014-12-22 at 11 25 36 am](https://cloud.githubusercontent.com/assets/674727/5529801/42477faa-89cd-11e4-8aae-8fc0388ada06.png)

I think we can use flex for this and the distinction won't matter. I believe one-row flex is supported in Gecko 18 (FxOS 1.1) so it should Just Work.