Update nav bar

[richleland]

Once Rich Guy has provided the logo and back treatment, we'll need to make the following changes:

• Need a link back to sp.com
• Need text or logo treatment to indicate this is the dev site, examples:
  • https://developers.pinterest.com/
  • https://developer.mulesoft.com/
  • https://code.exacttarget.com/
  • https://dev.twitter.com/

[colestrode]

There also seems to be an issue with the nav bar when using the back button. Step to reproduce:

• Open developers.sparkpost.com
• Scroll to the bottom of the page
• Click a link that takes you to another page (e.g., one of the github url's)
• Hit the browsers back button
• The nav bar will be have a transparent background and be hovering about 80% of the way down the page. Once you scroll, it will appear at the top of the page with an orange background.

This is probably an issue with the navbar jQuery plugin. It's probably listening for scroll events to know what the position is.