Device support: Introduce IDevice helper classes.

These are for configuration of process and ports gathering activities,
respectively.
This couples related functionality more tightly, while keeping
the number of IDevice methods at a reasonable level.
For ports gathering, the patch also adds the ability to configure
both the command and the parsing function; the latter used to be
hardcoded in the PortsGatherer class.

Change-Id: I1b8940397a51efa7ddc05dd15cf861777d118c1a
Reviewed-by: hjk <qthjk@ovi.com>