Draft: Resolve "Replace custom date functions with library `date-fns`"

Part of #153

I do not want to increase the MRs size further.
Therefore I propose these changes for now.
I tried to make the commits reasonable in itself - reviewing by commit makes sense imho.
I think more changes in the future might be beneficent therefore I would not close #153 for now.

Unused charts were removed - There were some issues because of accessed property _meta which does not exist in the type. If necessary once the functionalilty is used again the commit can be reverted - I did not want to spend time fixing linting issues on unused code.