Add V1.8 SKR V1.3 in SPI mode - needs PR#227 to work

[GadgetAngel]

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Add advanced setup of SPI mode for V1.8 SKR V1.3 This PR needs PR #227 so it can work properly. It contains a link to the information in PR #227

Placed in Community/Electronics: Update index.md of Electronics and added a new listing entitled "Voron V1 - BTT SKR V1.3 Wiring for both SPI and UART modes" create two new files:

1. v1_skr13_wiring.md - this talks about two modes for TMC drivers and provides links to other arears on the site to access the UART side of things and how to access the SPI setup;
2. v1_skr13_spi_wiring.md - this is the SPI setup;

reused the following from another setup: a. skrv13_RaspberryPi.md b. skrv13_Resources.md

• also added a hyperlink to a comparison TMC chart
• added a hyperlink to an article that discusses difference between SPI and UART
• added initial Removal of Jumpers pictures for SKR v1.3 in SPI mode
• Added Voltage Selections for SKR v1.3 in SPI mode
• added initial preparation - Set Jumpers diagram for BTT SKR V1.3 in SPI mode
• added a check box next to each item on the MCU description so the user can check of the items as he goes, if he wants. I had to enable the check boxes to be interactive by adding a JS function to thev1_skr13_spi_wiring.md file. New function called "enable_checkboxes();"
• added a term definition for BAT85 below the MCU description
• added section about Stepper Motor Drivers
• Added wiring diagram for Voron V1.8 BTT SKR V1.3 in in SPI mode
• Added the ability to download the wiring diagrams
• added the heatsink diagram to remind user to ensure that the heatsinks are installed on the stepper motor drivers in SP Mode
• added a note to help the user orient the heat sinks properly on the step stick boards.
• added a link that discusses BTT SKR V1.3 UART serial communications with Raspberry pi
• added SSR wiring diagram using BTT SKR V1.3 in SPI mode
• added the ability to download the SSR wiring diagrams
• added a link to skr v1.3 resources section that has the color pin diagram in it.
• compressed all pictures and diagrams so the page load time is fast.
• Checked these pages by running the server locally on my Windows machine, then if everything works, uploaded them to my LIVE TEST Voron Docs site at https://gadgetangel.org so I can see if there are any interactions between all the pull requests I have submitted thus far.