Add cancel button in ListPartNavigationAdmin.cshtml

[Bosseyang]

The added cancel button uses - href="javascript:history.back();" navigation back to the previous page.

This PR solves the issue #6666

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[Bosseyang]

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[Piedone]

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[Piedone]

You're not really canceling anything (unlike under content item editors); Simply "Back"? Also, I'd rather put in on the left side of this section, since it's navigation, not an action (an actual cancel would be like that).

[Bosseyang]

I agree! It is now changed in the latest commit: 9c0d5ce as per your suggestion.

[Piedone]

When a returnUrl is set, that should be used instead.

[Bosseyang]

Yes, we would have preferred to have used the built in returnUrl, but the problem is that in instances where we go two step further away from Content Items, it returns us and set us in an infinite loop due to how returnUrl works. For example:
Content Items -> Edit Blog (returnUrl = Content Items) -> Create Blog Post (returnUrl = Content Items + Edit Blog) -> Cancel goes back to Edit Blog (returnUrl = Content Items + Create Blog Post) -> Cancel goes back to Create Blog Post (returnUrl = Content Items + Edit Blog) ... and now we're stuck in a loop where clicking Cancel/back only adds then subtracts the returnUrl.

Hence we chose to solve it using: javascript.history.back

[Piedone]

Then that's what needs to be fixed, because going back in history is not universally correct.