Remove the need to register slash commands separately

We modified the slash command interface to allow getting command data, and created a generic implementation of it that automatically retrieves data from the command data. The interface should not be used now. Instead, extending the implementation is preferred as it provides a semi-working command already.

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

@@ -4,16 +4,22 @@ import net.dv8tion.jda.api.EmbedBuilder;
 import net.dv8tion.jda.api.entities.User;
 import net.dv8tion.jda.api.events.interaction.command.SlashCommandInteractionEvent;
 import net.dv8tion.jda.api.interactions.commands.OptionMapping;
+import net.dv8tion.jda.api.interactions.commands.OptionType;
+import net.dv8tion.jda.api.interactions.commands.build.CommandData;
+import net.dv8tion.jda.api.interactions.commands.build.Commands;
 import org.jetbrains.annotations.NotNull;
 import wtf.beatrice.hidekobot.Cache;
-import wtf.beatrice.hidekobot.objects.SlashCommand;
+import wtf.beatrice.hidekobot.objects.SlashCommandImpl;
 
-public class AvatarCommand implements SlashCommand
+public class AvatarCommand extends SlashCommandImpl
 {
-
     @Override
-    public String getCommandName() {
-        return "avatar";
+    public CommandData getSlashCommandData() {
+        return Commands.slash("avatar", "Get someone's profile picture.")
+                .addOption(OptionType.USER, "user", "User you want to grab the avatar of.")
+                .addOption(OptionType.INTEGER, "size", "The size of the returned image.",
+                        false,
+                        true);
     }
 
     @Override