Add Trident Mellow Flyf407zg in SPI mode; This PR will not work properly without PR #257

[GadgetAngel]

*Add Trident Mellow Flyf407zg in SPI mode, This PR will not work properly without PR #257 . It contains a link to the information in PR #257

*In Community/Electronics/ added the following:

1. GadgetAngel folder
2. images subfolder

updated Index.md file in Community/Electronics/ to add "Trident - Mellow FLYF407ZG Wiring for both SPI and UART modes" (tri_flyf407zg_wiring.md) tri_flyf407zg_wiring.md is a parent to tri_flyf407zg_spi_wiring.md

*reused three additional files: a. flyf407zg_additional_resources.md b. flyf407zg_RaspberryPi.md c. flyf407zg_Resources.md

added initial Removal of Jumpers diagram added initial preparation - Set Jumpers diagram for Mellow Flyf407zg in SPI mode Added description for Trident wiring diagram in Mellow Flyf407zg in SPI mode added the heatsink diagram to remind user to ensure that the heatsinks are installed on the stepper motor drivers for: Added the following MCU with heat sinks in SPI mode added URL to the Klipper Configuration by Antage(https://gist.githubusercontent.com/antage/1976d9df8e8a1126ebbe6f3935145394/raw/6bc4c53194be75a9889fba754ffa61fbb5c7cb89/printer.ini) for Mellow Flyf407zg informed use that the above config file needs to be changed from UART to SPI added links to other resources