Enhancement: Make default implementation (report filenames) more flexible.

[jbostoen]

Right now, we expect a reportdir and template parameter.

Use cases so far were simple: a "details" or "list" view of a specific class, usually the leaf class (PC, User Request, ...).
For convenience, we just had the template parameter where a name could be specified; and later a reportdir to override the "module" directory in which to look.

The new use case would require a report which can be used by a number of different (child) classes, and the main class (functional CI).