New faq page

New Splash pages for FAQs Customers and Merchants :-)

1. Meta Descriptions need writing for both FAQs pages.

2. @jamesshedden not sure how I should have set the colour for lists to grey - can u check?
.u-color-list {
  @extend .u-color-p;
}

3. Some links seem to have alt tags - maybe we can remove these? Also one has "target blank" - can we remove?

4. My section-heading class is still a bit messy - can we look at this together?

screenshots of the pages here:
![faq for customers gocardless](https://cloud.githubusercontent.com/assets/2903904/4402345/00ab6cda-4497-11e4-988d-0eabac646458.png)

![faq for merchants gocardless](https://cloud.githubusercontent.com/assets/2903904/4402347/0362728e-4497-11e4-8691-2f266cb089d8.png)

This should be `$header-color` - same as what `.u-color-heading` would achieve, but we'll include the colour in the `.section-heading` class for convenience