Add ".include" statement to scenario file

To avoid code duplication, the scenario file should accept an .include <path/to/file> statement. For instance, all model test files (scenarios) under directory VadereModelTests define the same topology. This could be avoided by reusing an existing topology description.

See following example for a scenario file with an .include statement:

{
  "name" : "scenario_with_include",
  "description" : "",
  "release" : "0.2",
  "processWriters" : {
    "files" : [ ],
    "processors" : [ ],
    "isTimestamped" : true
  },
  "scenario" : {
    .include "../topographies/ushape_obstacle.json"
    .include "../events/multiple_wait_events.json"
  }