Finish pr600: Added LEM-LTSR-NP footprint
Footprint to be used with LEM-LTSR6-NP, LEM-LTSR15-NP and LEM-LTSR25-NP. Symbol pull request https://github.com/KiCad/kicad-symbols/pull/615
This fixes the remaining points of #600.
https://www.lem.com/sites/default/files/products_datasheets/ltsr_6-np.pdf https://www.lem.com/sites/default/files/products_datasheets/ltsr_15-np.pdf https://www.lem.com/sites/default/files/products_datasheets/ltsr_25-np.pdf