When collaborating, cursor position is shared

[alepez]

Describe the bug
When collaborating, cursor position is shared: while user1 is pressing and user2 move the cursor over the canvas without touching, the pencil draw a line jumping from user1 position to user2 position.

To Reproduce
Steps to reproduce the behavior:

1. Open a collaborative lavagna in two different computers.
2. Start drawing and keep pressing on computer A
3. Just move the mouse in computer B
4. A line is drawn from position in computer A to position in computer B

Expected behavior

Nothing should be drawn when mouse is just moving without pressing in computer B, if A is drawing.