Cursor sometimes get stuck on click state causing the map to constantly move

[faucomte97]

Describe the bug
The cursor can get stuck on "click" status over the map window if the cursor moves to another window in-game mid-click.

To Reproduce
Steps to reproduce the behaviour:

1. Go to level 1 (or any other level).
2. Press down on the left mouse button on the map - don't let it go.
3. Move the cursor to the blocks area, to the left of the map. Let go of the mouse button.
4. Move the cursor back to the map area.
5. Notice that the map is still being dragged around despite you not clicking anymore.

Expected behaviour
The cursor status should keep track of whether you are clicking or not no matter which part of the screen you stop clicking.

[TomaszLaboj]

I'd like to work on this please , thanks

[faucomte97]

Good place to start for this task:

• looking at https://github.com/ocadotechnology/rapid-router/blob/master/game/templates/game/game.html to understand the layout of the game page