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/opencollective.svg

@@ -0,0 +1 @@
+<svg role="img" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><title>Open Collective</title><path d="M12 0C5.373 0 0 5.373 0 12s5.373 12 12 12c2.54 0 4.894-.79 6.834-2.135l-3.107-3.109a7.715 7.715 0 1 1 0-13.512l3.107-3.109A11.943 11.943 0 0 0 12 0zm9.865 5.166l-3.109 3.107A7.67 7.67 0 0 1 19.715 12a7.682 7.682 0 0 1-.959 3.727l3.109 3.107A11.943 11.943 0 0 0 24 12c0-2.54-.79-4.894-2.135-6.834z"/></svg>