Add max values for viaroute and trip and reorganize return code handling

"status" is now always:
 - 200 if the request was successful
 - 207 if the result is empty (no path found)
 - 400 if the request is invalid

 viaroute and trip now have a maximum of 500 and 100 locations
 respectively. Override with the --max-viaroute-size and --max-trip-size
 parameters.

include/osrm/libosrm_config.hpp

@@ -36,6 +36,8 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 struct LibOSRMConfig
 {
     std::unordered_map<std::string, boost::filesystem::path> server_paths;
+    int max_locations_trip = -1;
+    int max_locations_viaroute = -1;
     int max_locations_distance_table = -1;
     int max_locations_map_matching = -1;
     bool use_shared_memory = true;