contentlisting tile modifies sort_on/sort_reversed values of ICollection context

[petschki]

If you enable Mosaic's Layout behavior on a ICollection context and add a contentlisting tile, the sort_on and sort_reversed values of the contentlisting tile are saved on the ICollection context.

[petschki]

I tried to figure out how and why this is, but no luck so far ...

/cc @jensens @agitator @datakurre