Toolbar improvements

[cloverich]

Investigate:

1. Adding tooltip explaining what toolbar shortcut is when hovered; if it has a shortcut including the shortcut would be great

2. Make the toolbar sticky so it floats down as you scroll. I regularly need to scroll up when applying formatting to a longer document defer to Fixed toolbar #167

3. When a toolbar's styling is applied to the current selection, make the toolbar button "active" (this is built-in to the plate toolbar I think, but not working probably based on how I set it up)

[cloverich]

Implemented by #172