Add update, delete, add methods for absences

[Fermenade]

Hi,
here is some code that let's an user add, update and delete absences.

Changed some function names for clarity.
Added datatype representing the return type from untis
Added quality of life date time function
Added functions for add, remove and update operation

[ghost]

Unsafe parsing: In extractObjectByName, add a safety check for script.children[0].data. It will crash with a TypeError on empty script tags.
Error handling: Make the final throw more descriptive (e.g., "CSRF token object not found")
Timezones: Double-check if manual date-to-string conversion handles timezone offsets correctly to avoid shifts.

[ghost]

CSRF implementation is a necessary step, but its current stability is questionable. Fix the mentioned issues to meet the standard. We don't need more 'maybe-working' code in the core.

[Fermenade]

I'll take a look

[Fermenade]

Not sure how to do the type definition file stuff. Does anyone know? :)

[Fermenade]

@TheNoim just wanna check in. Do you see anymore problems in the code?