Quite a few things use dbus (plasma, hildon, ofono, connman,
networkmanager, etc) that I think it makes sense to just have this
started by default in pmOS rather than have every device package
implement this on their own.
In case someone shows up with a use-case, where dbus by default
is not desired, please speak up. Possible solutions are in #628.
This adds a custom swap file service, which allows specifying a
recommended swap size in the deviceinfo file via
`deviceinfo_swap_size_recommended`. For the N900 this defaults
to 1024 MB now. As the swap file is created in the root partition,
we have encrypted swap now (unless encryption is disabled with
`--no-fde`).
