Rename mock item scorer to precomputed
Add a list- or file-backed item DAO.
Implement an external process item scorer builder
Add user list user DAO
Make list of test users available to training
Improve efficiency of precomputed item scorer builder
Add missing license header
Refactor external algorithm test

Make item mean scorer more versatile, usable for the new external process builder
Test the external process item scorer builder

- Use external process item scorer builder in external-algorithms tests
- Add Pandas-based test that all 3 item mean scorers produce the same output
- Make python-pandas available in Travis environment
- Fix config properties in Gradle scripts
Reduce code duplication on process error handling
Deduplicate ID list reading code
Document new code & requirements
Comment bad interaction with component caching
Make external process deps transient
Add missing license header