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/paypal.svg

@@ -0,0 +1 @@
+<svg role="img" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><title>PayPal</title><path d="M7.076 21.337H2.47a.641.641 0 0 1-.633-.74L4.944.901C5.026.382 5.474 0 5.998 0h7.46c2.57 0 4.578.543 5.69 1.81 1.01 1.15 1.304 2.42 1.012 4.287-.023.143-.047.288-.077.437-.983 5.05-4.349 6.797-8.647 6.797h-2.19c-.524 0-.968.382-1.05.9l-1.12 7.106zm14.146-14.42a3.35 3.35 0 0 0-.607-.541c-.013.076-.026.175-.041.254-.93 4.778-4.005 7.201-9.138 7.201h-2.19a.563.563 0 0 0-.556.479l-1.187 7.527h-.506l-.24 1.516a.56.56 0 0 0 .554.647h3.882c.46 0 .85-.334.922-.788.06-.26.76-4.852.816-5.09a.932.932 0 0 1 .923-.788h.58c3.76 0 6.705-1.528 7.565-5.946.36-1.847.174-3.388-.777-4.471z" fill="currentColor"/></svg>