Bunch of personal changes to FlatUI.

- Sidebar has a blue border now. I didn't like that the current one
  blended in with the backgrounds on color schemes that didn't have
  colorful backgrounds, especially when the grid layout gets a 2px
  border.

- Selected tabs now have the background of the color scheme I use with
  this theme (forthcoming commit for that in Theme - Nil because it was
  originally made for that and I never bothered adding it) and blackish
  labels. I find this makes it easier to pick out the tab I'm using.
  Your mileage may vary on that.

- Dirty tab glyphs are no longer orange circles but white circles, just
  because a tiny orange dot on a blue background is pretty painful to
  look at. The white dot should be sufficient.

- Dirty selected tabs have a reddish tint to them and colored labels.
  Again, this may not be to everyone else's liking, but this is my
  personal fork, so ha.

- The find panel no longer has a middle-to-dark grey background because
  that made the find buttons physically painful to look at. Again, a
  case where red/orange on another color is not really a good choice in
  my book.

- All 'dark_content' attributes are set to false because this is very
  clearly a bright theme.

- The minimap overlay color is now a middle-grey color, as I needed to
  change it because of my color scheme of choice. Again, I don't use a
  colorful background in views.