Toolbar: Remove call to _setOptions from inside _makeFixed

Note by @gabrielschulhof: Edited commit message to
comply with new style guide and replaced author with real name.

Fixes gh-6567

**Note:**
This PR also reverts the part of 86b70c6510c759ebc8f474a992c8e23b2c33a1c7 that prevents a second button from being added, and includes a test to make sure a second button is not added. IOW, this is the right way to fix #6554.