Toggle for plaintext wrapping.

[max-nextcloud]

When using plain text files users should be able to decide if they want lines to be wrapped or not. This should be implemented using a toggle. The toggle state could be remembered in the browser storage.

Either wrapping or not wrapping will not work for everyone or every file type / content. Having a toggle is quite common for a text editors.
Originally posted by @juliushaertl in #1407 (comment)

We also do not have a menubar in plaintext view so the ui is fairly simple anyway.

[julien-nc]

@max-nextcloud Do we still want to implement that? If so, do we set it to high so it's done for the next release? I'm adding the tag, feel free to remove it 😁