Centralize the URI and the ID string parse/build code

This also reduces the code duplication and consolidates the behavior
between QtContacts and QtOrganizer.

Change-Id: Ia2df252e6b55652821df143c1421b326bfbc3c7f
Reviewed-by: Matthew Vogt <matthew.vogt@qinetic.com.au>
Reviewed-by: Christopher Adams <chris.adams@jollamobile.com>
Improve Q*Id autotests a bit

Change-Id: Ib679d291c62e85e85b1887e31d642deef70e31c2
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Reviewed-by: Christopher Adams <chris.adams@jollamobile.com>