Make breadcrumb model static after specified time

[iche033]

depends on ignition-gazebo pull request #90

Add disable_physics_time param to breadcrumb plugin that turns the breadcrumb model static after ~3 sim time seconds. A static entity is created when the model becomes static, and that indicates to the comms broker that it should update its visibility graph.

You should see output similar to this:

[Msg] Deploying X1__breadcrumb___0 at 3.55 5 0.13228 0 0 0
[Dbg] [EntityComponentManager.cc:627] Using components of type [285520019272511910] / [ign_gazebo_components.DetachableJoint].
[Msg] Breadcrumb 'X1__breadcrumb___0' is now static.
[Dbg] [Physics.cc:864] Creating detachable joint [729]
[GUI] [Dbg] [EntityComponentManager.cc:627] Using components of type [285520019272511910] / [ign_gazebo_components.DetachableJoint].
[Msg] New breadcrumb detected, visibility graph updated

Signed-off-by: Ian Chen [email protected]