Slider block - add slides to beginning / middle

[SophieAmnesty]

At the moment if you want to add more slides to an existing slider block, you can only add them to the end of the slides.

If you want to add a new slide at the beginning of the slider, or in the middle, you have to rebuild the whole thing again and add the slides in the correct order.

It would be cool if it was easier to re-order slides within a slider and to add new slides wherever you want.

note: this was raised by a section site admin in the user survey