Draft: Resolve "Add carry over feature for lessons and supervisions"

Closes #31

added part::backend part::frontend source::customer::engs type::feature labels

assigned to @hansegucker

added 1 commit

• f2844b4c - Add copy methods for whole validity range

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@ZugBahnHof Could you please a. test this and b. adapt the frontend to the changes?

@yuha checks that now

...together with @ZugBahnHof