Bug 658331 — Ensure read-only PersonaStores have empty writeable-properties

Bug 658331 — Ensure read-only PersonaStores have empty writeable-properties

Ensure that Edsf.PersonaStore.always-writeable-properties is empty for
EDS address books which are read-only. Similarly, ensure that
Edsf.Persona.writeable-properties is also empty for such address books (which
follows because it passes through the value of always-writeable-properties).

No other backends need modifying for this, since no others have a concept
of “read only” except libsocialweb, which already has empty
writeable-properties properties.

Closes: bgo#658331