MS0301: implement simple tools

[idhamari]

The implementation for these tools is the same: we call

 opensim-cmd run-tool  file.xml

For now, we need only two functions: load xml file and run. When running the tool, the result file is loaded and the model should be animated in the visualizer. I will provide a complete example when we start working on this task.

This applied to all the tools menu except:

• plot:
• scale
• convert
• plugins

In a later milestone, we will visit this menu again and implement the tools in a similar way to the java interface.

[idhamari]

This task has less priority and is ignored for now!