R1:555c0421bb35

Allow slugs to contain most utf8 characters

Summary:
Ref T2632. Fixes T1466.

Currently, we normalize slugs (and thus Phriction URIs and canonical project names) to a small number of latin characters. Instead, blacklist a few characters and permit everything else (including utf8 characters).

When generating Phriction URIs, encode any utf8 characters. This means we render URIs encoded, but browsers handle this fine and display them readably in the URI and address bar, etc.

The blacklisted characters are…