Update material icons reference URL

[craigreyenga]

The current URL for the material design icon reference is: https://materialdesignicons.com/

This redirects to a new URL, and presents an alert indicating that it has moved.

The updated URL is https://pictogrammers.com/library/mdi/

[BPowell76]

The library needs to also be updated. The project is using version 5.8.x and the now deprecated webfont. I may try to see how to update it, but I'm a noob web developer.