New and updated Mursten-era parts

[Magnus Forsberg]

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Garage door and frame
The studless garage door frame with tabs for slotted bricks is not in the library. There are two variants, both to be submitted, with proposed numbering:

• 821a.dat: with full tabs
  
• 821b.dat: with partial tabs
  
• The existing 821.dat should be renumbered 821c.dat and "with Studs" should be added to its name.
  

The correct door for this period is 822a.dat. However, with all the various counterweights in the library, none is the correct match. They should have pin holes and they are a different shape.

• Should these be new suffixed variants (R and L) of u9187, or given a new base number?
  
• These would be combined with the door into a new shortcut, 822ac02.dat.
  

I reworked all the garage doors. Do you have any images of the missing versions?
821.dat is in need of some corrections, if it's reworked.