Fix #compare_with for file scopes

The default Machinery::Object#compare_with implementation considers
the whole object different if one of the attributes differs. In the case
of file scopes there are two attributes, though, which can differ
between the compared objects independently (:extracted and :files).

The new implementation in FileScope - which the scopes inherit from now -
compares those two attributes independently from each other which
results in more reasonable diffs.

Fixes #339
Raise an exception if a FileScope contains unsupported attributes
Show extraction status in config-files renderer
Show extraction status in changed-managed-files renderer

In case of compare it is also possible to have scopes with no files
= nil so some checks were needed to prevent issues.
Show extraction status in unmanaged-files renderer
Remove extraction status from the general renderer

Since the extraction status is now shown by the scope specific renderer
it was removed from the general.
The reason for this change was that the extraction status should be
comparable and the header of wasn't shown in compare.
Update NEWS file for new release
Merge pull request #376 from SUSE/fix_comparing_file_scopes2

Fix comparing file scopes2