Updated the design and GL properties of layers

[rasagy]

• Already existing traffic signs (in OSM) are shown as larger dots:
  1. Light blue for Traffic lights
  2. Red for Stop signs
• Added new color palette for the different states of the traffic sign being reviewed:
  1. Signals that have not been reviewed are in yellow
  2. Signals that are existing are marked as reviewed, and show up as light grey (with the above two types of OSM orbs behind it)
  3. Signals that are invalid (No Signal) show up as dark grey
  4. Signals that are added after review show up as teal
• Tweaked styling for Mapillary layers (lower opacity for icons, thin green trails), tile boundaries (lighter red, center aligned tile numbers with size ramps), highlighted roads (lighter grey)

Overall, the goal for a reviewer should be to remove all yellow nodes from the map. :)

cc @ajithranka @planemad Can you have a look if this works?

[rasagy]

Got a review from @ajithranka, will go ahead and merge this for now. Will improve the styling further based on feedback from @bsrinivasa, @poornibadrinath & team.