Add License file to reference licensing for used imagery

LICENSE-IMAGES.md

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+Adding this file here, as some of the imagery used in the Schema modules were not created by me, and thus must be referenced appropriately:
+* XMPP: Released under the [MIT Expat License](https://commons.wikimedia.org/wiki/Category:Expat/MIT_License "MIT Expat License"). [Source](https://commons.wikimedia.org/wiki/File:XMPP_logo.svg "Wikimedia")
+* IRC: Released under the [Creative Commons Attribution-Share Alike 3.0 Unported license](https://github.com/fabianalexisinostroza/Antu/blob/master/LICENSE "CC-SA 3.0 Unported"). [Source](https://commons.wikimedia.org/wiki/File:Antu_irc.svg "Wikimedia")
+* Slack: Released under the terms of [Slack's Branding Guidelines](https://slack.com/brand-guidelines "Slack's Branding Guidelines"). [Source](https://brandfolder.com/slack "Slack Icons @ BrandFolder")