Hard Drive Stackable and HotSwappable Caddy 3.5"

This is a remix from https://www.thingiverse.com/thing:3708393

I really like the original design :
* it's simple
* it doesn't consume too much material
* stack is stable

But it doesn't permit to remove disk easily because :
* On some HDD like Seagate 18To, stack connectors are blocking the HDD. So it can't be removed without un-stack the upper caddy.
=> So, I've place connectors it a little bit higher.

* We can't grab HDD easily (we have to push it from the back)
=> So, I've made a free space to be able to take the HDD.

I've keep stack connectors placed at the bottom, in order to install it at the top of an existing stack.