Changed colors of navigation path and start/destination markers when getting directions

[sharon-ho]

What has been changed:

• Navigation path was previously blue which was a bit jarring to the eyes, but now it is the color azure which is easier on the eyes and resembles that of the mockups
• An easy workaround to indicate directionality is to have the start location marker be a different color from the destination location marker and for those colored markers to be icons next to the location names at the top
• Custom markers may be considered for future improvements

[sharon-ho]

@gdzooks I decided to have AZURE_COLOR as a constant rather than have a variable called PATH_COLOR storing the hex code for azure since I think it makes more sense to have a reference list of all colors used in the project in one place. Also, if the color is re-used elsewhere in the future, there wouldn't be a need to duplicate the hex code in another constant. Even if we don't make another constant with the same hex code, it wouldn't make sense to use PATH_COLOR for something that isn't a path despite it having the color azure.