Avoid infinite loops and optimizations

[jledentu]

This PR adds some optimizations and improvements:

• Reduce performance bottleneck in the layout algorithm when the chart contains a lot of datasets, by setting a loop limit. This can lead to overlapping labels when there is a LOT of labels, but anyway in this case the chart may not be readable
• Improve the resizing algorithm to fit the labels in the chart area, by running successive fitting processes
• Avoid to draw labels if fitting is ongoing
• Rewrite the collision algorithm by making it more readable