feat: marker should be kept stored between slide changes

[mateusfccp-cos]

Description

Currently, disabling the marker erases it. We should keep it on screen and prevent it from erasing when moving between slides. This way, if one advances and goes back, the marking will be already there. It should be only cleared when manually doing so.

Requirements

• Disabling the marker shouldn't erase it
• Moving between slides shouldn't also clear the marker