How to Add a variable

To add a variable like "LAMBDA" do the following

1. add it to variables.h file in KRATOS "includes, in a similar way to anyone of other variables that are there (kratosR1\kratos\includes);
2. add it to variables.cpp file in KRATOS "sources" directory (kratosR1\kratos\sources);
3. change the corresponding application interface in "custom python" file;