Cleanup Sources class

Signed-off-by: Tomas Hozza <thozza@redhat.com>
Cleanup setup script functions in Sources class

Signed-off-by: Tomas Hozza <thozza@redhat.com>
Add constant for /dev/null into ProcessHelper

Signed-off-by: Tomas Hozza <thozza@redhat.com>
Sources: implement build, install and clean functions

Signed-off-by: Tomas Hozza <thozza@redhat.com>