June changes from Communications committee 

As detailed in https://github.com/ciudadanointeligente/home-poplus/issues/50.

![screen shot 2014-06-20 at 10 48 12](https://cloud.githubusercontent.com/assets/739624/3338747/2ea77a1c-f860-11e3-92f9-05b4096d3fe5.png)

The "Get Involved" and "Components" pages now have sub-pages. The the "PoplusCon" pages have been renamed to "Conference" (I've kept the URL slug as /popluscon, however, to avoid broken links).

This pull request also includes a fix for the CSS / Sass for the header, since I think the last person to edit it accidentally edited the generated CSS, and not the Sass source. There is now better documentation in the README, so hopefully the same mistake won't happen again.