Fix two errors in parsePandaURLsText

We should not call fixProposedContactName on existing contacts, but
doing so actually pointed out that I'd been using a random character
where I wanted a random lettter.
Fix scoping error deleteSocialGraphRecords

A local id prevented deleteSocialGraphRecords from deleting anything
Use opaque URI format

Repalce the pond-introduce-panda://NAME/SECRET/IDENTITY/ URI format with the
opaque URI format pond-introduce:NAME?pandaSecret=SECRET&identity=IDENTITY