Rename DFN/QFN generator, add new footprints

Created by: Ratfink

The DFN/QFN library has been renamed to Package_DFN_QFN.pretty; this renames the generator script to match.

This also adds two new footprints: QFN-36-1EP_6x6mm_P0.5mm_EP4.1x4.1mm and QFN-48-1EP_7x7mm_P0.5mm_EP5.6x5.6mm, needed for STM32 chips.

External PRs:

• https://github.com/KiCad/kicad-footprints/pull/504
• https://github.com/KiCad/kicad-footprints/pull/505