Remove memory leak from MarkerClient

While the internal that.markers map did not have duplicates, the rootObject.children list still remembered a reference to the old marker and thereby prevented the garbage collector from eating it.
Merge pull request #56 from knowrob/patch-1

Removed memory leak from MarkerClient
add tfPrefix for multi-robots support
Merge pull request #57 from rk4an/devel

add tfPrefix for multi-robots support
Added LINE_STRIP and LINE_LIST support
Fixed linting errors
allow to change cellSize
Merge pull request #59 from rk4an/patch-1

allow to change cellSize
Merge pull request #58 from mszarski/patch-1

Added LINE_STRIP and LINE_LIST support to Marker.js
Urdf shapes fix

Now you can draw other shapes.

Example, try:
roslaunch urdf_tutorial display.launch model:=urdf/05-visual.urdf
rosrun tf2_web_republisher tf2_web_republisher
roslaunch rosbridge_server rosbridge_websocket.launch

and open on browser: examples/urdf.html
Correction on measure unit for cellSize

the difference between last revision end now using the familiar SI unit:
"cellSize" in meter and "Size" is number of cells. More similar a grid object on rviz
Merge pull request #61 from Vegekou/patch-2

Correction on measure unit for cellSize
Merge pull request #60 from Vegekou/patch-1

Urdf shapes fix