refactor: architectures.

Adds dnf.arch, with great fanfares removes dnf.rpmUtils.arch. The inisght is
that DNF does not really need to know about the arches, with the ocassional
exception of basearch.

Related: RhBug:1072972
drpm: output stats (RhBug:1065882)

I could go further with callback interfaces etc. but this is simple and
working now.
New version: 0.5.1
build: 0.5.1-1
bin/dnf: run the python interpreter with -OO.

Cheaply shaves off <100 ms from e.g. 'dnf upgrade'.
packaging: cosmetic: copyright years in bin/dnf.