Blender Git Loki

Rename App Menu to Blender Menu

"App" is a name reserved for the application templates at the moment.
It may become its own term in the near future if Templates are separated
from "Apps".

So since this is a name not exposed to the users we should renamed it
sooner than later.

Note that this will require scripts to update since the name of the
class is renamed here.

This also requires an update in the User Manual.

Differential Revision: https://developer.blender.org/D12523