Setup for a png-based ipynb app backend

This is just the app stuff, but I think Kaftan already
has the rest more or less finished. If we combine the
two, we have an actual IPython backend!
ipynb app: we *can* be not available.
ipynb-app: fix style and not available
ipynb app: rename to ipynb_vnc
arg flake
ipynb app: dont use glut as a back-backend

This should prevent the stalling of Travis I hope
fix to last commit
Merge pull request #297 from almarklein/ipynb-app

Setup for a png-based ipynb app backend