New wallabag installer

Instead of the legacy bin/install here is a symfony command that can initialize wallabag.

There are still work to do on the requirements part (to be sure that wallabag can run like a charm).

I've also added (but commented) the fixtures load part (which will need an extra doctrine package). We'll see that point later.

app/build.xml

@@ -9,7 +9,6 @@
     <target name="prepare" depends="clean" description="Prepare for build">
         <exec executable="composer">
             <arg value="install"/>
-            <arg value="--dev"/>
             <arg value="--no-interaction"/>
             <arg value="--working-dir=.."/>
         </exec>