[#29325123] Model properties

Squashed commit of the following:

commit 97f625e580ce6a062bb9fd37fefc11b5568e9d8d
Author: Sebastian Pape <email@sebastianpape.com>
Date:   Thu Apr 11 15:34:56 2013 +0200

    finish feature for model properties

commit 1cb98dd145fb7f70a5608d4229117b7e02e5143c
Author: Sebastian Pape <email@sebastianpape.com>
Date:   Wed Apr 10 15:48:32 2013 +0200

    put model categories in the right place

commit 7203aa4322b8df736e130592f4ba1e0909192aba
Author: Sebastian Pape <email@sebastianpape.com>
Date:   Wed Apr 10 15:38:16 2013 +0200

    implement sortable model properties