Improvements for multiple selection tool

[HDeiro]

Using the multi-select widget on Chisel (print below), I feel like it would be good if:

• Already selected options were filtered out (avoid dupes);
• Allows multiple selection at once (clicking on each one of them and reopening the select is quite boring;
• Give an option to select all/clean all;
• Maybe it would be possible to use a little bit better the horizontal space to not be sooooo vertical (another image is attached as an example)