Replace JS code in HTMLs by global function calls

Currently, a lot of elements in our HTML contain plain JS code. @amer1 suggested that we could reduce this code to function calls and define the functions globally for the TIDO page.

This issue adds the JS functions. In a separate issue in https://gitlab.gwdg.de/subugoe/eupt/eupt-xml/ all JS code has to be replaced by function calls.

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