Updates to nav and responsive layouts

Bringing back in the old Bootstrap fixed nav as the other was not playing nice with Scrollspy. Going to experiment with bringing in some of the JS and some of the styles from http://tympanus.net/Blueprints/AnimatedHeader/# rather than all.

BS3 is mobile first so set up conferences-theme.scss accordingly and added some WIP styles for mobile and larger desktop breakpoints. Current state:

![screenshot 2014-02-03 00 19 59](https://f.cloud.github.com/assets/3168960/2063227/a4c05314-8cb2-11e3-8b08-331e9b70f3c9.png)
![screenshot 2014-02-03 00 20 10](https://f.cloud.github.com/assets/3168960/2063228/a4c30b9a-8cb2-11e3-9df7-db68d56be2fb.png)
![screenshot 2014-02-03 00 20 23](https://f.cloud.github.com/assets/3168960/2063229/a4c3dcdc-8cb2-11e3-9717-ee1a9c5d098f.png)
![screenshot 2014-02-03 00 20 32](https://f.cloud.github.com/assets/3168960/2063230/a4c4135a-8cb2-11e3-90ff-d83945cd24cf.png)