Adds a visualizer as described in #2

src/main/java/net/knarcraft/stargatecommand/command/VisualizerTabCompleter.java

@@ -0,0 +1,44 @@
+package net.knarcraft.stargatecommand.command;
+
+import net.TheDgtl.Stargate.network.RegistryAPI;
+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;
+
+import static net.knarcraft.stargatecommand.util.TabCompleterHelper.filterMatching;
+
+/**
+ * A tab completer for the /sgc visualizer command
+ */
+public class VisualizerTabCompleter implements TabCompleter {
+
+    private final RegistryAPI registryAPI;
+
+    /**
+     * Instantiates a visualizer tab completer
+     *
+     * @param registryAPI <p>A reference to the registry API</p>
+     */
+    public VisualizerTabCompleter(RegistryAPI registryAPI) {
+        this.registryAPI = registryAPI;
+    }
+
+    @Nullable
+    @Override
+    public List<String> onTabComplete(@NotNull CommandSender commandSender, @NotNull Command command, @NotNull String s,
+                                      @NotNull String[] args) {
+        if (args.length < 2) {
+            List<String> networkNames = new ArrayList<>();
+            registryAPI.getNetworkMap().values().forEach(item -> networkNames.add(item.getName()));
+            return filterMatching(networkNames, args[0]);
+        } else {
+            return new ArrayList<>();
+        }
+    }
+
+}