Add costmap_2d package sources

Convert navigations/costmap_2d from gitlink to normal tracked files.

navigations/costmap_2d/cfg/GenericPlugin.cfg

@@ -0,0 +1,7 @@
+#!/usr/bin/env python
+
+from dynamic_reconfigure.parameter_generator_catkin import ParameterGenerator, bool_t
+
+gen = ParameterGenerator()
+gen.add("enabled", bool_t, 0, "Whether to apply this plugin or not", True)
+exit(gen.generate("costmap_2d", "costmap_2d", "GenericPlugin"))