Added EtaCorrection method for 3 hit clusters.

In Cluster.py:
- added eta correction method for L shaped 3 hit clusters
- this improves the 3 hit cluster resolution by about a factor 2 (see plots)

To do in the future:
- optimise the added fourth pixel tot (currently 1) to minimise the resolution.
May need to be a different value for different thicknesses. May need to be a
different value depending on tot of three other pixels.
Added fit info to res plots.

In ComputeAlignment.py:
- removed unneeded scaler definition

In pyEudetAnalysisOnly.py:
- added fit information to res plots
Final version of Anne-Laure's Cluster.py code.

Small changes, comments and tidy to the existing Cluster.py code written by Anne-Laure.
I plan to make some changes to the EtaCorrection method, and wanted to document a final
version of 'how it used to be'.
Merge pull request #18 from sredford/master

Added EtaCorrection method for 3 hit clusters.