Change the current/not current mechanism by a no_readings_timeout parameter, so layer is not considered current until this timeout is elapsed without new sonar readings
[SonarLayer] Install costmap plugin file
Added initial gitignore
Install the sonar_layer lib
Renamed sonar layer to RangeSensorLayer

Since it nicely covers both sonars and IR sensors
Rebased on corot:catkinize

While here:
- renamed topics_namespace and topic_names_list into 'ns' and 'topics'