Add LED_PLCC-4_3.2x2.8mm_KKKA

I'm really not very sure about this one, and would appreciate some guidance.

I want to use this LED: Osram LS E63B

It uses a 4-pin PLCC-4 package, and connects 3 of the pins to the cathode, and one pin to the anode. Because the PLCC-4 is a pretty standard package, I opted to make this a generic footprint to allow for other LEDs that use this package in this way, and to allow use of the standard LED symbol which only has two pins. I followed the convention used in the Diode library of adding a "KKKA" suffix to denote the usage of the four pins. However, I'm unsure whether this is the best way of going about this. I'd be happy to revert the footprint to a vendor-specific one if this is the preferred way of doing it.