Move command handling out of constructor, add coin reflip command

Having heavy code run in a constructor is bad practice. We made separate methods for command handling.

src/main/java/wtf/beatrice/hidekobot/commands/slash/AvatarCommand.java

@@ -12,7 +12,7 @@ import java.awt.*;
 public class AvatarCommand
 {
 
-    public AvatarCommand(@NotNull SlashCommandInteractionEvent event)
+    public void runSlashCommand(@NotNull SlashCommandInteractionEvent event)
     {
         event.deferReply().queue();