LGS tip-tillt correction

[GillesOrban]

This PR concerns the following:

• Fix typos concerning LGS spot elongation
• LGS image should not be flipped (line 400-402 in base.py). Can be seen in correlation map, e.g. for an on-axis launch the central slope variance should be minimum (if no obscuration, central slopes should be close to 0 for similar launch aperture and subaperture).
• WIP: Correction of LGS tip-tilt is now possible using a combination of removeTT=True, correctLgsTT. At the moment this may not be fully realistic but helps to stabilize the LGS on a Shack-Hartmann. Comments are welcome.

[codecov-io]

Codecov Report

Merging #98 into master will decrease coverage by 0.17%. The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
- Coverage   66.93%   66.75%   -0.18%     
==========================================
  Files          24       24              
  Lines        3920     3950      +30     
==========================================
+ Hits         2624     2637      +13     
- Misses       1296     1313      +17

Impacted Files	Coverage Δ
soapy/confParse.py	81.79% <100%> (+0.1%)	:arrow_up:
soapy/wfs/base.py	62.75% <48.14%> (-4.5%)	:arrow_down:
soapy/wfs/shackhartmann.py	86.51% <83.33%> (+0.19%)	:arrow_up:

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