Suggestion: introduce Fluent icons

[Mark Spencer]

I feel like the UI could be improved by replacing the current icons with Windows Fluent icons. The current ones do not render well, produce sharp and inconsistent edges, some are too complex for such a small scale. Windows fluent icons are completely open source and can also be modified. 

https://fluenticons.co/

I replaced the current icons with the fluent icons, just to see what it would look like. Also:

Repositioned the bottom left icons in the groups panel to the center of the panel (before it was aligned to the left main windows edge)

Moved the folder navigation icons down a little, so the space between item count and file/folder list is even. This was done in 30 min.