Various dark mode problems

[nephele]

• Replicant dragging on the destop has badly visible lines, This likely needs a more comprehensive fix, since it intersects with the functionality of background images.

• Window top bars have gradients that are too bright

• BTab has gradients that are too bright

• BTab devider (between inactive tabs) is not visible

• pref/Appearence colors of font preview don't live update

• aboutSystem colors don't live update

• There is no visible border between TextFields and panels when both are the same color (also a light mode problem?)

• Button gradients are too jarring in dark mode, should be more gradual. (same with BTitleColumnView)

• Some Icons use Dark lines as design elements making those not visible (pref/appearence, pref/network, pref/sounds, demo/sudoku)

• Shine on window borders on the tab does not match the window (It looks like the window tab is one pixel too far on the left because of the shine)