Initial basic functionality commit

What this commit adds:
* Ability to apply a theme, given a folder
* Extract all .zip files in /Themes/ into a relevant folder
* Get all theme metadata from info.smdh
* Proper unicode handling

What's still needed for initial release:
* Theme shuffling
* GUI

source/linked_lists.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include "3ds.h"
+
+struct theme_data;
+
+typedef struct
+{
+	struct theme_data *data;
+	void *next;
+} node;
+
+void add_node(node*, node*);