install IPython 2.x in docker image

allows nbviewer to render v4 notebooks
Merge pull request #362 from minrk/2.x

install IPython 2.x in docker image
add missing RUN
fix installation of IPython 2.x

pip install git+... doesn\'t get submodules right for 2.x
add numerical PDE solver example
Merge pull request #364 from waltherg/master

Add example that demonstrates how notebooks can be used to derive and implement numerical algorithms
Link to developer.rackspace.com when linking RS
Merge pull request #365 from rgbkrk/rackspace_link

Link to developer.rackspace.com when linking Rackspace
update bokeh link to new repository
Merge pull request #366 from chdoig/patch-1

update bokeh link to new repository
Added Gitter badge
Merge pull request #367 from gitter-badger/gitter-badge

Add a Gitter chat badge to README.md
adding /slides prefix for rendering as reveal
cleaning up multiple exporters
fixing redirects
template cleanup
handling gist_id to user/gist_id
adding some basic tests
replacing all icons with fontawesome
using youtube-play for slides