Add tiled map, tilesheet configs etc

These are just XML so relatively git-friendly.  They're needed for the
game and should be syncronised to the version of the code so they
really ought to be checked in.

assets/templates/house.tx

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<template>
+ <tileset firstgid="1" source="../objectsprites.tsx"/>
+ <object type="2" gid="3" width="80" height="80">
+  <properties>
+   <property name="animframes" type="int" value="1"/>
+   <property name="assetpath" value="/obj/house.png"/>
+  </properties>
+ </object>
+</template>