Merge branch 'projectproperties' into 'master'

Merge branch 'projectproperties' into 'master'

Fix project.properties dependency issue

Correctly place scrlib references also
in the case there is no project.properties file
present in the original repository.

This commit fixes a problem, which was introduced with
021df3c42420de542bf11f22948831023b47ebf3: If no
project.properties file exists in the original
project's source repo, place_srclib will not place
a dependency --- even if there should be one:

>    if not os.path.isfile(proppath):
>        return

Example app: fdroiddata/metadata/org.berlin_vegan.bvapp.txt

See merge request !47