Attach tools for individual planning groups

[romanarust]

Currently, it is possible to attach a tool to the robot via robot.attach_tool(tool, group=groupname) to the end-link of the planning group. However, it only works with one planning group: If I want to attach another tool to another planning group, it get's detached from the first planning group. (robot.attached_tool gets overridden). Also, robot.detach_tool() does not allow to pass a group name.

[chenkasirer]

Opened https://github.com/compas-dev/compas_fab/pull/356 in an attempt to address this issue by making Robot.attached_tools a dictionary which maps a planning group's name to it's attached tool.

However, the robot.attach_tool() also sets the Tools ToolModel in the RobotArtist associated with this instance. There, multiple tools don't seem to currently be supported. In addition, I am not 100% sure if collision detection even supports adding the meshes of multiple tools (or if it even makes sense) and not sure how to test it.

@gonzalocasas @romanarust maybe you have some input on the above.

[gonzalocasas]

Done in #356