Improved gaussian2d estimator

[Geegee]

Trying to improve the estimator for the 2 D gaussian fit function

Description

Transform the recorded counts into a probability distribution.
Estimate mean and variance from that.

Motivation and Context

Can help when the photon source moved quiet a bit from the previous
position.

How Has This Been Tested?

On the dummy. Ideally this would get some testing in action.
Although the method to estimate was already used in the old qudi.

Screenshots (only if appropriate, delete if not):

Types of changes

• Bug fix
• New feature
• Breaking change (Causes existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• I have documented my changes in /docs/changelog.md.
• My change requires additional/updated documentation.
• I have updated the documentation accordingly.
• I have added/updated the config example for any module docstrings as necessary.
• I have checked that the change does not contain obvious errors
  (syntax, indentation, mutable default values, etc.).
• I have tested my changes using 'Load all modules' on the default dummy configuration.
• All changed Jupyter notebooks have been stripped of their output cells.