This commit introduces the Pythonic reimplementation of mentat-reporter-ng module. It is complete from roughly 70 percent, there are many features that stil need to be implemented as well as some necessary polishing.

The most important next implementation steps:
* thresholding and relapse
* email template improvements
* report section legends with translations
* report web interface improvements
* unauthorized access to reports
* unit testing and bulletproofing

(Redmine issue: #3378)