various updates for ipyvuetify

[maartenbreddels]

• fix import of missing Timer
• remove dead code
• provide solution of the exercise
• add example of making a new widget on the fly

[mwcraig]

@maartenbreddels -- does jupyter-veutify need an update for jlab 1? I'm getting this in console when I try to run:

Error: Module jupyter-vuetify, semver range ^0.1.3 is not registered as a widget module

[maartenbreddels]

I hope it is fixed tomorrow morning