Complete implementation of new caching system, and extend

[fkuehlein]

New caching was introduced with 93ab748 and merged with #219. See commit message for description and hints on how to proceed.

As a first step towards this: (EDIT: resolved as of #236)

The pylint check 'no-member' is currently disabled globally. Working on re-enabling it on 196-review_linting, but would trigger warnings in TestCached as well as RecurrenceNetwork and subclasses. In the latter cases, the old caching is still in place (see above linked commit). Should be reviewed and tested for.