Add facet for public demos

[grtjn]

Make it easier to find demos with a few checkboxes, grouped top-left under 'Miscellaneous', including:

• Publicly showable (new public property, to mark demos that can be shared with wide public)
• Running at customers (existing internal/external dropdown)
• Unrestricted (restriction property or behind vpn)
• Does not require internet (new offline-capable property)

[bluetorch]

@grtjn will these be facets on four new properties, or do any of them already exist?

[mariannemyers]

I believe we already have one for 'restricted' demos.

[grtjn]

I updated the description to clarify..

[grtjn]

PR #252 allows easy extension of list of search checkboxes with pre-defined queries. That works well to cover all filters we are looking for. Adding all filters suggested above requires touching data as well though. I'll leave this ticket open, and first deploy #252.