Add color and lanes to ramps

[1999michael]

Description:
Make ramps in IGVC world more realistic by getting the right color and adding white lines to the edges of the ramp.

Goals:

• Have correct IGVC ramp color to all 4 ramps (look on google images for correct color--darkish green)
• Have white lanes on the left and right side of every ramp

Acceptance Criteria:

• White lanes must connect for connecting ramps
• All 4 ramps in IGVC world should be correct color (darkish-green)

Notes:

• Check out SDF file structure at http://gazebosim.org/tutorials?tut=model_structure