Render canvasses as HTML with `slackdump view`

[tlhr]

Is your feature request related to a problem? Please describe.
The view output is great and mostly comprehensive, but it would be even better if channel canvasses could be rendered in a similar way – they are not always linked to in messages.

Describe the solution you'd like
Maybe rendering canvasses with tabs across the top of the channel, just as in Slack itself.