add notebook loader and custom template

[lzfxxx]

No description provided.

[lzfxxx]

Related reviews are in origin pull request #210 (which mixed some unrelated changes, so I closed it)

[lzfxxx]

Moved from #210
jonashaag: my_full? Confusing name :-D

lzfxxx: It's just a little CSS modification of nbconvert template 'full', cause the width in @media setting of that template will make the html overflow the markup div. The naming is not very clear, do you have any suggestions?

jonashaag: I see! In this case could we simply use the default template and add the CSS fixes to klaus' CSS file? Or if that doesn't work, can we use inheritance to override the CSS instead of copy-pasting the whole file?

[lzfxxx]

fixed

[lzfxxx]

Moved from #210
jonashaag:
In terms of security, XSS problems are possible at the least. So we have to account for that. Two ideas:

• Apply a very restrictive Content Security Policy for the whole klaus application, and have 2 versions of .ipynb file viewer: a normal CSP-enabled version, and a a CSP-disabled version. We could toggle between them with a simple URL param e.g. ?nocsp.
• Maybe we can use this SanitizeHTML preprocessor, haven't looked at it closely. Also we could have two versions of the viewer page, one which strips all <script>, <style>, <object> etc tags, and another one where everything is allowed.