Updates to main setting page UI

[dhowe]

Settings UI could be better - currently the horizontal line at bottom appears to be the end of the page and makes the export options difficult to find. Comparison to ublock (which uses lines between ALL sections) below.

Items:

1. remove horizontal line, add lines between all segments OR move line to very bottom
2. remove inactive expert mode, and add 'expert-only' options button or link

full-height on a 27" monitor:

zoomed-out:

[mushon]

I agree, let's do it like uBlock does it.