Refactor instances -> elements and improved examples and docs

[DaJansenGit]

This brings some changes which would be better placed in seperate branches but where needed in this for easier development, I'm sorry for the mess:

• some improvements regarding examples and documentation in form of a template plugin that allows to give an example without the usage of any "real" plugins
• the refactoring of instances --> elements as this is confusing for the users as we also named the classes elements.
• split up the PrepareBPS task which was not really specific to one goal into the tasks FilterTZ and ProcessSlabsRoofs.
• bump python to 3.10 (solve problems with geomeppy and eppy compability with 3.10, see #602 which I mergend into this branch for testing purposes)
• make sure that docs are build in CI even if tests fail

[DaJansenGit]

@Cudok I fixed the problem with the tests. This is ready for review.