Blender Git Loki

Fix ugly alignment of "Mono" option in the Sequencer

Steps to reproduce were:
* Open Sequencer, add a sound strip
* In the sidebar, open the Adjust > Sound sub-panel
* Note the placement of the "Mono" item

The layout code would disable decorators if a property came from a
non-animatable data-block type. Doing so would mess up the alignment
where properties from different data-block types were be mixed.
This is not the case any more.

Note that when actually adding the decorator, a blank icon is inserted
to keep the alignment intact when the data-block type isn't animatable.
So the decorator is still not shown, but the alignment looks fine.

This may affect more cases. If so, and if that's an issue, the
decorators should be explicitly disabled.