add the machanism of lateral tunneling near the gate (non-orthogonal tunneling)

- NEW : add a new parameter for non-orthogonal tunneling near the gate
- NEW : add a new class to deal with lateral tunneling
- ENH : enhance the previous method for loading band structure, checking if lateral tunneling occurs
SimCTM directory and file names are now environment dependent.

- NEW : add new class for environment-dependent file paths