Navigation - (menu) activity

Pls see the flow in this link:
https://zpl.io/dxDzzNK

In content step (#2)
There is a new tab: navigation with buttons
https://zpl.io/7wkrkBq
https://zpl.io/Z09Z91L

They behave as images, except:

1. They have shades
2. Hover state is 70% transparency on the player.
3. Double click on a button opens a text box on the button.

Menu buttons-20220411T130803Z-001.zip

In interaction step (#3)
The teacher selects a button to add navigation to.

1. The teacher can select activities from the list.
2. Each activity line has 5 states: regular, hover, linked, linked-hover and disabled.
3. The activity of where we are (navigation) is disabled.
4. Once an activity is selected a blue icon appears on the left upper corner of the button on the canvas, and on the line of activity on the panel. https://zpl.io/nolwlEA
5. On hovering on the linked activity a hyperlink icon to unlink appears. https://zpl.io/PqzZz7M
6. when no activities yet, an error notification appears: https://zpl.io/qyZpZem
7. In case the teacher linked an activity and later on deleted it, an icon of a broker link appears. Same icons appear on the activity line on the panel. https://zpl.io/L4kyk0B