Fix inconsistent donation icons and add OpenCollective (#609)

resolved #608
* fixes Inconsistent donation icons and colours #608
replaces all donation png's with svg's from https://simpleicons.org
removes svg files with "-svg" at the end

* fixes the issues due to vscode formatting the code

* fixes Discord icon
fixes some formatting errors, caused by copy& from the previous commit with wrong formatting

* fixed else-if's
added Open Collective Icon
I couldn't find the icon for the Economy Category from Feather

* added unknown_donation.svg
replaced unknown donation icon
removed old unknown.svg icon

* renamed unkown donation icon for consistency

* somehow the cmmits before didn't add the new Icon
Fixed formatting issues (again)

* fixes formatting issues (I need to look into that)

* fixed else-if's that somehow got reverted

* Fix lint

* Strict equals

* Fix lint again

assets/images/external/kofi.svg

@@ -0,0 +1 @@
+<svg role="img" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><title>Ko-fi</title><path d="M23.881 8.948c-.773-4.085-4.859-4.593-4.859-4.593H.723c-.604 0-.679.798-.679.798s-.082 7.324-.022 11.822c.164 2.424 2.586 2.672 2.586 2.672s8.267-.023 11.966-.049c2.438-.426 2.683-2.566 2.658-3.734 4.352.24 7.422-2.831 6.649-6.916zm-11.062 3.511c-1.246 1.453-4.011 3.976-4.011 3.976s-.121.119-.31.023c-.076-.057-.108-.09-.108-.09-.443-.441-3.368-3.049-4.034-3.954-.709-.965-1.041-2.7-.091-3.71.951-1.01 3.005-1.086 4.363.407 0 0 1.565-1.782 3.468-.963 1.904.82 1.832 3.011.723 4.311zm6.173.478c-.928.116-1.682.028-1.682.028V7.284h1.77s1.971.551 1.971 2.638c0 1.913-.985 2.667-2.059 3.015z" fill="currentColor" /></svg>