Individual tool settings

I like to set the Fill tool to UV Map and the Brush tool to project to work on seams and gaps, but changing the settings in one of the tools also affects the other. Would be cool to be able to adjust the settings of each tool individually.

No files, tests, or entry points are named in the issue. Start by locating the Fill and Brush tool setting definitions and how their current values are stored; done means changing one tool's settings no longer changes the other's, while both tools retain their individual choices.

Written by the indexing model from the issue text.