Do not use matplotlib for testing contains

Extracting the coordinates using the method from #17 is incredibly low. This PR reverts the changes and instead of using the matplotlib artist to test if it contains the event, we calculate the maximum distance in x and y, and if the distance to the closest grid cell is larger than this maximum dist, we do not use it

• Tests passed (for all non-documentation changes)
• Fully documented, including CHANGELOG.rst for all changes