Improve variable inspector.

[niconomaa]

• remove mock data
• fix variable updating

[niconomaa]

inspector works for all user defined vars and ignored polyglot.

pieces of functionality of the inspector we might be interested in and should discuss:

• language of origin (or last used) for var
• code cell of origin (or last used) for var
• detailed inspectiom of objects

[niconomaa]

design is more in line with rest of jupyter now