Add elliptic cut

Add an elliptic cut allowing to cut on arbritrary 2D quantities
around a mean position with elliptically dependent X/Y-widths.
Extend group cut  by a nand

Extend the group cut to allow an additional nand condition.
Modify sum function to allow for subtraction.

Add the possibility to subtract quantities. This is done by putting
and additional list of subtrahends to the config file. It is also
possible to use this function to change the sign of a variable.
Add sqr to basic calcs

Add sqr template function to basic calcs which also to calculate the
square of a quantitiy.
Merge pull request #1 from tproc12/master

Improve several cuts and functions.