Channel summary page

[jvansanten]

We generate summaries of the transients updated in the previous night for each channel, like in
this example. These can be rendered into a channel overview page. This should show:

• A sky map of the transient positions, following this example. The onclick event should link to the lightcurve viewer for that channel and transient.
• The summary rendered into a simple table whose rows link to the lightcurve viewer.
• Links for next and previous nights.
• A link to download the raw JSON summary.