Clean up the PIC microcontrollers mess

In accordance with the suggestions [reported here](https://lists.launchpad.net/kicad-lib-committers/msg00246.html).
* All duplicated symbols has been removed.
* The microchip.lib library contain only an ENC28J60 (all packages).
* The microchip_pic32mcu.lib library has been created and PIC32MX575F-TQFP64 has been moved to it.
* Remove the whole library microchip1.lib. Unique symbol PIC18F8448 has been removed - this device doesn't exist (result of typo in part name).
* The microcontrollers.lib contain only MCUs other than those manufactured by Microchip. Unique PIC18F452 has been renamed and moved to microchip_pic18mcu.lib.
* Update unique symbols to match Library Convention.