Should fix #300:
1. Modifying preprocessor so that every bootcamp entry in _config.yml always has a URL field.
2. Modifying other code to always rely on this.
Merge pull request #311 from gvwilson/fixing-bootcamp-urls

Should fix #300: bad bootcamp URLs in calendar.
Navbar work
* mostly the collapsed the bar, make less awkward
* some link colour changes
navbar & links
* input from @r-gaia-cs
* links on hover: darker & underline
* move search bar to bottom on collapse
Fixing Mozilla Science Lab logo in "About Us"

The svg logo of Mozilla Science Lab use some special font that can
be unavailable in some machines and for that reason we should use
a png version of it.

Similar problem had been report in #250 and fix in #254 for home
page and now we fix it to "About Us".
Merge pull request #316 from r-gaia-cs/fix-logo-about-us

Fixing Mozilla Science Lab logo in "About Us"
Change header case for @r-gaia-cs
Merge pull request #315 from acabunoc/master

Navbar - make smaller screens a bit prettier
Why not a MOOC?
Merge pull request #317 from gvwilson/blog-why-not-a-mooc

Why not a MOOC?
Adding 'Best Practices' paper to bibliography
Merge pull request #318 from gvwilson/adding-best-practices-to-bibliography

Adding 'Best Practices' paper to bibliography
Updating wording
Merge pull request #320 from gvwilson/changing-wording-of-mooc-post

Updating wording of MOOC post - @kaythaney confirmed wording by email.
Update gem installation instructions.

- Remove `gem install redcarpet`. Redcarpet was an external dependency
  until Jekyll 1.1.0 was released 2013-07-14.
- Add `gem install RedCloth`. RedCloth is required for Textile
  templates in _includes/disqus.html and _layouts/badges.html.
Merge pull request #319 from goxberry/remove-redcarpet-gem-from-readme

Remove `gem install redcarpet` from README.md.
Making a couple of posts favorites
Merge pull request #327 from gvwilson/adding-favorite

Making a couple of posts favorites
Updating airports for instructors