Provide List of changed files

[jastram]

This is a follow-up issue on #487 . @MarcBehrens requested a list of changed files. Here is a mini-spec for what we intend to do:

1. We will create a second status file (e.g. status-files.txt) and leave the old one running.
2. The underlying mechanism will be the same as specified in Requirements: Model-building CI #487 .
3. Like the initial implementation, the file will grow, rather than being replaced.
4. The file format is as follows:

File Format

• 1st Line: Timestamp
• Subsequent lines: filenames, relative to the root of the git repository, one path per line. There will be no encoding, e.g. spaces stay space. The file is UTF-8 encoded.
• Followed by an empty line

[jastram]

This has been realized.