adds phone number to contact sales lead capture form

Another experiment to try to maximise the number of people contacting sales. This time I'm adding an option to call sales at the bottom of the contact-sales form just in case ppl don't want to give their details away to the internet.

![screen shot 2014-12-02 at 14 03 32](https://cloud.githubusercontent.com/assets/5781410/5263711/2ffeccaa-7a2c-11e4-8ddc-346acdd56a20.png)

@almonk what do you think of this (both the idea and the appearance)?

cc @benmiller169