Few fixes to the sensor type code.

In ComputeAlignment.py:
- removed unnecessary line future_builtins.SensorType= "Timepix" before checking
options.sensor
- fixed bug in print statement (wasn't printing!) regarding 180 degree rotation

In Constant.py:
- made the comment more specific to avoid confusion with Timepix = Timepix1 and
Timepix = all kinds of Timepix chips
Added control plots to ComputeAlignment.py

In ComputeAlignment.py:
- added two plots (before and after alignment) showing the track-cluster
distance. They help to determine the cuts that should be applied in
FindMatchedCluster. Plots are saved in the root file.
Added resolution plots to ComputeAlignment to better see quality of alignment.

In ComputeAlignment.py:
- added total and 2hit cluster resolutin plots to the end, to be able to see the
quality of the alignment as soon as it's finished, without having to run
reconstruction and analysis seperately. Plots are saved in rootfile. Results are
printed at the end of the alignment process.

Note: I realise that this is alot of 'code' in what should just be a user script.
In the future it might be good to hide the code in a function, but currently no
MakeResolutionPlots exists.... in pyEudetAnalysisOnly.py the plots are also made
here instead of being resuls of a function.
Added a Z angle optimisation function to ToolBox.py.

In ToolBox.py:
- added a function which finds the optimal Z angle of rotation
- replaced the old 'starting Z' finder in Perform3StepAlignment with this

More details:
The old 'starting Z' finder used to step through -1 to +1 degrees,
calculating the metric every hundredth of a degree. This takes 200-300
(and more?) seconds per iteration - current code uses two iterations.
New minimize code takes around 60 seconds the first time, then 30 seconds
the second time.

I checked the results of the alignment when using the old and new Z finder.
I looked at three runs from three different sensors, all results are compatible.
For two runs the new Z finder produces a marginally better result, for one run
it's slightly worse. I think that on the whole, resolutions are equivalent and
the new Z finder is much quicker. Also possibly more robust, as the Z angle
could be outside the 1 degree limit and would still be found, unlike before.
Merge pull request #22 from sredford/master

Few updates to the alignment code.