New functions for Artist Model

[mehulsinha73]

Expected functionality in the Artist Model.

• Labels/settings can be attached to an agent. Labels can be the name of the agent or an overridden value.
• Labels/settings can be positioned anywhere on the artist canvas.
• Attached labels/settings will move along with the agent they are attached to.
• Visibility of labels/settings can be toggled on/off (either manually or zooming in / hovering on an agent)

Tasks:

• Create a new render_text function in default_drawers which calls the render_text function for the visualization engine.
• Modify init() in Artist to handle value of labels and possibly have labels/settings on a different layer