reading MeshCat.jl and peripheral libraries

[HiroIshida]

package hierarchy

MeshCatMechansim: RigidBodyDynamics, MeshCatGeometry, MeshCat MeshCatGeometry: MeshCat, RigidBodyDynamics

Resolve issue related loading pr2 mesh file

.obj file process flow: MechanismGeometries:URDFVisuals -> MeshcatMechnism:MechansimVisualizer -> MechanismGeometries:visual_elementgs -> same:parse_link! -> same:parse_geometries

the mesh file is passed toMeshCat:MeshFile`

why some parts are not shown

package path list has only directories for ros packages...

Example: pr2_descrption/meshes/base_v0

load sequence: base.obj -> base.mtl

[HiroIshida]

possible pull request

1. here must include 0.9