Blender Git Loki

Rename "Make Asset" to "Create Asset"

The term "make" in this context refers to modifying an item to obtain a certain
property. Creating an asset however means saving a copy of a data-block as
asset. So "create" is better suited here.

Generate preview when making a data-block an asset

Initial "Make Asset" operator

Accessible via the Outliner context menu (ID Data submenu).

The operator currently copies the data-block and creates empty asset data for
it. This will later contain all the meta-data to "give the data-block meaning".

Of course there are many TODOs and questions remaining. This is the first step
so I can work more on meta-data support.
I created some files and that I think make sense.