Web GUI: Replace Dropdown for car, bike, foot selection with three icons

[foss-]

Currently
The dropdown is difficult to handle and requires several clicks.

Expected
Offering a bike, car and foot icon and display all three icons instead of the dropdown would make for much easier and quicker handling. Keeping the blue background in combination with white icons should provide good visibility.

[frodrigo]

Please report it to https://github.com/Project-OSRM/osrm-frontend

[foss-]

Of course: Project-OSRM/osrm-frontend#335