[libcommhistory] Add event statuses for incoming messages

These are negative values to avoid changing any existing value in the
enum (which breaks database compatibility) or adding values larger than
the error values, which may break some code.
[libcommhistory] Add messageParts and subject roles to EventModel
Merge pull request #75 from special/mms-event-status

Small API tweaks
Bump rpm and pkgconfig version due to API changes
[libcommhistory] Add MmsHelper QML object

This exposes MMS-specific event functionality using various dbus
interfaces.