Tidy descriptions of PLCC4 LEDs

• Add sizes to keywords
• Add size codes (resolves !3136 (closed) - 3.2mm x 2.8mm LEDs are also called 3528, which includes the leads to arrive at 3.5mm)
• KICAD6 -> KICAD7 in 3d paths
• Fix a couple of broken datasheet links

Let me know if I can standardise the descriptions/keywords more. In particular is "common anode" useful when applicable?