Improve map output for better diff-viewing with mapeditor xml output

[gurkenlabs]

Although our exported XML maps can be opened with the mapeditor, the output XML differes in a lot of ways.
Some properties are being serialized in a different order and some have a different type (double instead of int).

It is desired to adjust out output in order to improve intercompatibility between the tools.

Example:

current:

<object gid="0" height="21.0" id="162" type="PROP" width="20.0" x="694.0" y="315.0">

desired:

<object id="162" type="PROP" x="694" y="315" width="20" height="21">