Have Brush Styles remember color settings

[MMachado05]

On Xournal++, I'm quite used to switching between my highlighter and pen tools with the convenience of knowing my highlighter will still be yellow when I go back to it, regardless of the color of my pen. On Rnote, however, the color setting exists at a "higher hierarchy" than the brush style, so it's applied globally. Per-brush style color settings would make switching between the highlighter and pen tools significantly easier!