Implemented the mentat-informant.py module (previously mentat-briefer).

The mentat-informant.py module is a Python replacement for previous mentat-briefer.py module. It is designed to provide periodical statistical overviews via email. The email reports are localized using babel package and can be translated into any language. Additionally, the reporting engine uses Jinja2 templating system for message rendering, so it enables very easy customization. (Redmine issue: #3377)