Mobile nav fixed.

Now shows links instead of 'undefined'.
removed Twitter configuration for timeline and follow buton which are no longer integrated
Fixed GitHub jsonp call. Closed #1118
Merge pull request #1116 from peterboni/patch-1

Mobile nav fixed.
added config_tag plugin for integration of configuration into templates
Merge branch 'master' of https://github.com/imathis/octopress into source
updated from upstream