fix maths for working distance def and oil depth

fixed up maths, knowing working distance is really
the distance the lens can see after the coverslip
of correct thickness...
rather than the whole distance from lens to sample focus,
which is wrong definition
this changes how the oil distance is defined, its
WD - distance
in the design case of correct coverslip thickness
but the more complex
WD - distance + coverslipdesigned - realcoverslipthick
in the aberrated case.

updated version to v 0.2 to reflect that large change.
update maths from last commit to oilCalc.py

Add the oilCalv maths

use the fix in the latest version v0.2 of the python oilCalc.py
now gets maths right as working distance definition is correct
and so oil thickness calc is right.

Working distance  for 60x/1.42 is correct,
others are wrong, need to find thm out and fix

also temp and wavelength corrections are still to do
so i disabled the sliders, greyed out. using disable flag
of jquery mobile slider.