Makes a whole lot of changes

Adds some new tests
Improves plugin command handling by using one class for each command
Makes some changes to vehicle teleportation to support horses and pigs, but vehicle teleportation is still buggy and messy
Adds some more missing comments
Adds a wildcard permission and uses built-in permissions some places to avoid checking for three different permissions

src/main/java/net/knarcraft/stargate/command/StarGateTabCompleter.java

@@ -0,0 +1,23 @@
+package net.knarcraft.stargate.command;
+
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.command.TabCompleter;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class StarGateTabCompleter implements TabCompleter {
+
+    @Override
+    public @Nullable List<String> onTabComplete(@NotNull CommandSender commandSender, @NotNull Command command,
+                                                @NotNull String s, @NotNull String[] strings) {
+        List<String> commands = new ArrayList<>();
+        commands.add("about");
+        commands.add("reload");
+        return commands;
+    }
+
+}