Adding an index.html in core pack. Adding the xx-XX.localise.php and index.html in the install.xml

As title says. When making a core pack we now get these 2 files correctly.
```
[...]
<filename>fr-FR.localise.php</filename>
		<filename file="meta">install.xml</filename>
		<filename file="meta">fr-FR.xml</filename>
		<filename>index.html</filename>
```