[Feature] Update collection from the web-ui

[Abrynos]

Use-Case:

Sometimes I'm on a non-synchronized device (such as a work laptop) and don't have my phone on me. It also happens that in this scenario I might learn new information about someone, which I want to add to my contact information. In such scenario I'd like to be able to use the web-ui to re-upload an existing collection (after downloading and manually editing the vCard entries) without having to manually delete the collection first (and then uploading it, paying attention to the href).

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Implementatoin:

My first idea is a new button in the "Edit Collection" view that opens a file-picker and a confirmation dialog afterwards, though I'm open for other suggestions.

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I'm willing to contribute the code for this feature if you're willing to accept a merge request for it.
(In such case, since I don't know the codebase yet, I'd appreciate a small pointer towards the files/folders I need to take a look at)

Thank you in advance for considering the inclusion of this feature.

[pbiering]

Technically it's an overwrite of an existing collection (which requires permit_overwrite_collection = True or O permissions in rights).

Implementationwise one has to check existing javascript client to execute required DAV calls.

Code extension on server side should be hopefully not required.