Fix pqStringVectorPropertyWidget to support utf8 strings.

The problem is described in ticket #0014729.
UTF8 chars were not correctly converted (toLatin1()) was used
so TextSource for instance were not able to support accentuated
chars.

Change-Id: Ia527552c230351364541ddff2e9a527784bed976
Merge topic 'Fix_utf8_issue_for_StringVectorPropertyWidget' into next

99501ea4 Fix pqStringVectorPropertyWidget to support utf8 strings.