"Sort by" menu should have checkmark for current selection

[colejd]

When you open the "sort by" menu, we denote which mode is selected by dimming the rows that aren't the current selection, with the icons representing each mode on the right. I propose two adjustments to improve readability:

• Move the icons to the left, before the text.
  • This will make it easier to associate the icon with the text, and make room for my next proposal...
• Use a checkmark to denote the current selection. This would go where the icons used to be, along the right side.
  • This improves legibility. Dimming the other cells as we do now reduces contrast too much, and it makes the cells look disabled.

[tejuamirthi]

Hey @colejd is it up for grabs? If yes, I'd like to takeup this issue. Thanks!

[colejd]

Let's see if @ccrama likes the idea, since it's more of a design request from me than an actual todo.