Expand Notebook 7 acceptance tests

[bollwyvl]

Elevator Pitch

Add additional robot test cases to test features such as markdown preview factory integration, multidocument navigation (such as it is).

Motivation

#54 adds a bare minimum sanity check for notebook support, sufficient to get out a alpha (#55), but lacking testing of corner cases (which should probably be tested independently).

Design Ideas

*** keywords ***
verify a notebook factory can be navigated
  [arguments]   ${factory}=Markdown preview  ${document}=README.md   ${slide_count}=7  ${subslide_count}=2

toggle notebook zen mode
   Log    determine what this might mean