Fix Travis-CI and Appveyor for ZEF and CPAN modules

[softmoth]

So long as GitHub is used for the repo_url, this allows ZEF and CPAN
modules to display the Travis and Appveyor status.

Note: In order to re-check Travis status for distributions erroneously marked as 'not set up', this commit either needs to be tagged with [NEWDB], or else have something like this SQL run on the main database:

update dists set travis_status = 'unknown' where dist_source != 'github';

The following changes were needed:

1. Fill in repo_user and repo for all sources that have a github url

2. Store $dist->{files} as Perl data, not as a JSON string. This makes
   it useful while building the object. Marshalling to JSON is done when
   writing and reading from the DB, rather than repeating the from_json
   anywhere the data are needed.

3. Generate a similar $dist->{files} entry for Source::GitHub dists.

4. Modify Appveyor and Travis post-processors to use the files hash
   instead of the GitHub-specific {_build}{files} array.

[JJ]

This probably needs a rather extensive review... that includes tests. Please give me some time to take a look.