Importer not importing the templates for collision shapes

[Flavien]

Plugin version: 2.3, downloaded from GitHub

Issue description
When using templates for collision shapes in Tiled, the shape gets imported as empty into the tileset.

Steps to reproduce
Using tiles like this:

 <tile id="717" terrain="16,21,16,16">
  <objectgroup draworder="index" id="2">
   <object id="1" template="Top-Right.tx" x="8" y="0"/>
  </objectgroup>
 </tile>

With Rop-Right.tx containing:

<?xml version="1.0" encoding="UTF-8"?>
<template>
 <object name="Top-Right" type="area">
  <polygon points="0,0 24,0 24,24"/>
 </object>
</template>

What gets imported is a RectangleShape2D with an empty extent: