UI changes for responsive layout on small screens

This pull request addresses a number of issues:

- Site header is too wide on small screens [#44](https://github.com/symphonycms/factory/issues/44)
- Footer elements overlap on small screens [#45](https://github.com/symphonycms/factory/issues/45)
- The .get-symphony class is too wide for small screens [#46](https://github.com/symphonycms/factory/issues/46)
- The background on the .network-nav doesn't work so well for small screens [#47](https://github.com/symphonycms/factory/issues/47)

Happy New Year! :D