New condenser for upright to use LED PCB

This merge request updates the upright condenser to match the new condenser for the inverted microscope. It enables use of either 5mm LED or the circular OpenFlexure LED PCB

From #270 (closed):

This would involve:

• Make the Z position parametric, closing #227 (closed)
• Split the upright condenser into two parts - a part similar to the inverted condenser (but without the mounting) and an "lid" that includes the objective mounting wedge to connect to the Z axis.
• Add in the holes to the "lid" to allow the existing 5mm LED holder to fit there
• Increase the size of the void under the condenser (i.e. at the top of the lid) to allow use of the illumination PCB
• Add a lug to the condenser that enables the existing mounting screws to be used, possibly in the opposite direction (i.e. screwing through clearance holes in the condenser, into tapped holes in the lid/mounting.

---

also required:

• renders for building the illumination
• instructions

closes #270 (closed)
closes #227 (closed)

docs/finished.md

@@ -9,7 +9,8 @@ Congratulations, you have now assembled your OpenFlexure Microscope.
 ![A render of the completed microscope](renders/complete_microscope_{{var_optics, default:rms}}2.png)
 ![A render of the completed microscope](renders/complete_microscope_{{var_optics, default:rms}}3.png)
 
-Your completed microscope should now look like these pictures.
+Your completed microscope should now look like these pictures.  
+There is also an [interactive 3D view](interactive_3d_view_{{var_optics, default:rms}}.md) of the finished microscope.
 
 ## Software set-up {pagestep}