Improvement to M^2 Measurement

[sunjerry019]

Currently, the setup:

1. Finds the center
2. Finds the Z_R
3. Measures the M^2

The M^2 measurement may be sped up by

1. Taking rough measurements of the beam caustic
2. Doing a fit to obtain rough Z_R and center measurements
3. Taking a few more measurements within the +/-Z_R range.
4. Doing a refit

This reduces the total number of measurement points significantly.

(Idea from Thorlabs)