Show error about length for too short names

[friedger]

Currently, the browser does show names as "already taken" for names that are too short. Looking up the name result in "invalid_name", which is not the same as "already taken".

The browser should indicate that the name can't be registered.

Example: oichat.id.blockstack (id.blockstack requires names of 8+ characters)

[ryanarndtcm]

This also impacts .id names as well