[PyWB2] /collinfo.json to be compatible to old version

[sebastian-nagel]

The /collinfo.json must be compatible to that shown by an index server running with PyWB 0.33.2. Users have built tools relying on:

• the given format
• a guaranteed order of collections (newest coming first)

Cf.

• http://index.commoncrawl.org/collinfo.json
• http://index-pywb2.commoncrawl.org/collinfo.json

[sebastian-nagel]

Adressed in commoncrawl/pywb@3705514 (note: should be configurable whether or not to use the template engine).