Issue 1609 - Handle the case of no selectors in "Block Element"

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extra : rebase_source : c8689c0d6cb3839ca8e162f27f0f09c8cf4c4668
Issue 1610 - Don't remove overlays before the "Block element" dialog is closed

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extra : rebase_source : 2b1a273704e609cc4d43278821d3929dabe4596f
Issue 1612 - Remove prisoner when user blocks an element with an overlay

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extra : rebase_source : e825e17cd7422ddffb3d5daaf46c5fe34cd95f8f
Issue 1613 - Don't collapse elements with non-HTTP URL

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extra : rebase_source : f485fde05664cdd72c2a04263cb8fe736e7355f7