Added FiniteDifference Method for TEM. Hardcoded atm, needs UI option adding to make it selectable.
Added UI option to swap between full3D and FD. Still only enabled it for TEM though.
Added UI options for setting slice thickness and changing number of integrals for full3d method.
Simulation now simulates atoms up to Z=103
Merge pull request #92 from ADyson/FiniteDifferenceMethod

Finite difference method