rework mime types, support pasting file lists, SIP when dropping single files

src/sdl_clipboard_utils.hpp

@@ -3,4 +3,10 @@
 // returns the mimetype (c-string) of the image in the clipboard
 // or nullptr, if there is none
 const char* clipboardHasImage(void);
+const char* clipboardHasFileList(void);
+
+bool mimeIsImage(const char* mime_type);
+bool mimeIsFileList(const char* mime_type);
+
+// TODO: add is file