Assembly: Initial implementation (#10427)

* Assembly: Initial implementation.
* Disable Assembly wb as it's WIP.
* Stub code for handling assembly import.

Co-authored-by: sliptonic <shopinthewoods@gmail.com>
Co-authored-by: Paddle <PaddleStroke@users.noreply.github.com>

src/Mod/Assembly/assembly.dox

@@ -0,0 +1,4 @@
+/** \defgroup ASSEMBLY Assembly
+ *  \ingroup PYTHONWORKBENCHES
+ *  \brief Tools to build assemblies
+ */