Improve tests and functions dealing with config reading/writing

[rwinterschlaf]

Currently default-based tests are thrown off if a user-generated config exists. Config writing has not been turned into a test yet. Thus this issue encapsulates the following areas:

• config writing
  --> more importantly: making tests unintrusive to running collections; perhaps through a placeholder URL that does not actually lead anywhere and gets deleted again after testing
  --> add a config retriever option that immediately chooses the default config, even if user config exists (could be good for testing)
  --> implement format guidelines that throw errors if a user does not following them (i.e. www. .de instead of https://www. .de/)
  --> make a TEST!
• TEST: correct config being chosen
• Rinse and repeat for metadata configs

In this vein, also test out if PK's idea to have the default configs as .py with dicts in them works and stops problems from popping up.

[FlxVctr]

would refrain from having configs as .py files, as they're more prone to user error/less user friendly.

Besides that, pytest has built-in functions for temporal directories that could be used for testing.

[FlxVctr]

https://docs.pytest.org/en/6.2.x/tmpdir.html

[rwinterschlaf]

All functional so far - tests check for default and user created homepage and metadata configs. Not sure how to proceed in the field of the metadata config. Would an interactive fill-out click function (as with the homepage config) be sensible?

[rwinterschlaf]

• decide on whether an interactive fill-in prompt function would be useful or too much of a hassle for the user
  @FlxVctr thoughts?

[FlxVctr]

It's a nice convenience function, but depends on how much time you have to spare

[FlxVctr]

A function to create and open a well commented template file might be quicker to develop, less error prone and easier to maintain in the future