Stylesheet Fixes for v1.5
    
    - Fixes scene cast when floating showing wrong border color around panel
    - Color correction for Neutral theme scrollbar handles
    - Removes minor code duplication
    - Makes menu icons and indicators a little bit more symmetrically spaced out to the text and menu box
    - Fixes sporadic bug seen in Linux with tree list branch icons, sometimes the default Qt icons show, sometimes they don't, setting a transparent image instead of empty URL seems to solve it
    - Color correction to better differentiate child and mesh columns in darker themes
    - Restore dark column color for FX