Fix residuals for AAMs

Now AAMs are hardcoded to take the SSD. Also, renamed LSIntensity
to SSD.

Also, removed the optimisation choice for LK as it was useless
anyway since only GN was implemented.
Update base.py

Add a note about the limitations of residuals to SSD with AAMs
Spelling mistakes in @jabooth comments
Merge pull request #478 from patricksnape/residual_aam_fix

Fix residuals for AAMs