Rename the dynamic_graph namespace in dynamic_graph_manager

[MaximilienNaveau]

Problem

The namespace inside the dynamic_graph_manager is not called properly. A better encapsulation of things is actually needed.

Potential solution

• rename the dynamic_graph namespace in dynamic_graph_manager
• encapsulate the ros things in a dyanmic_graph_manager_ros namespace.

[MaximilienNaveau]

Related to this PR https://github.com/machines-in-motion/dynamic_graph_manager/pull/22