This is a soap plate, which you can easily remove.
There is a clamp for the shower's bar. This design is for bar around 22.1cm of diameter. I can adjust the dimension if needed, this is an easy tweak, so don't hesitate to ask.

 I will soon share the files, I just want to clean it up, and make some tiny changes first.

Installation :

Take both clamps, and tighten them around the shower's bar. You will need 2 M3 nuts, and 2 M3X12 (or M3X10 if it works for you) screws. Once installed, you can simply slide the plate onto the clamp. This process makes it much easier to clean, or replace if needs be.

This model includes two holes, to avoid making a soap bath. There's a slight slope towards the holes, although FDM printing makes it kind of useless. 
There's a bumpy part, for your solid soap.
Another hidden features of this model, is that it includes small slits on the inside. This forces the slicers to add walls inside the part, and makes it stronger, without loosing too much print time. See the picture for a better understanding of this.

In the future, I plan on adding something that would allow you to hook a small cloth on it. (I don't know the name in english please help me out. It's the cloth you take into the shower to help clean yourself, it's sometimes like a glove.)
If you have other suggestions, please go ahead. I'd be glad to hear your thoughts.

Printing:
I have printed this in PETG. ABS or ASA should work fine. PLA can work too, but may not be a durable option.

The plate is 150x220mm wide, but there is a second version, which I haven't really tested. It's 150x175, to allow Prusa mini and Bambulab a1 mini's to print this model.

Print this file in its normal orientation. You will need support for the clamp's slot.