[teregen] Add overview for stored coverage data
With the implementation of poo#90401 the template generator is no longer stateless, hence there is a need for managing stored data and/or edit them directly. I propose to create a simple web page as a part of the template generator to list all data used in the creation process. This page can provide a simple interface to delete any no longer valid entry from the database. As the amount of data will grow over time, a filter/search function would be needed.