Replace RJ45 jack by Würth 7499010121A

This one appears to be readily available at various distributors.

Also add 3D print models for case parts, obtained from

https://www.eevblog.com/forum/projects/diy-dsoxlan-interface-for-keysight-oscilloscopes/msg4323214/#msg4323214

apparently authored by Jay_Diddy_B.

Adapted layout to fit these models.

DSOXLAN.pretty/Spacer2b.kicad_mod

@@ -0,0 +1,22 @@
+(footprint "Spacer2b" (version 20221018) (generator pcbnew)
+  (layer "F.Cu")
+  (fp_text reference "REF**" (at 0 -0.5 unlocked) (layer "F.SilkS")
+      (effects (font (size 1 1) (thickness 0.15)))
+    (tstamp 19a86c51-d154-44ce-88a7-a2c0b00d75c1)
+  )
+  (fp_text value "Spacer2b" (at 0 1 unlocked) (layer "F.Fab")
+      (effects (font (size 1 1) (thickness 0.15)))
+    (tstamp 4267d8d5-efc3-47d7-b494-d8c9cdda981d)
+  )
+  (fp_text user "${REFERENCE}" (at 0 2.5 unlocked) (layer "F.Fab")
+      (effects (font (size 1 1) (thickness 0.15)))
+    (tstamp 3f0abedf-3c43-4805-99bb-3a9f33a249ea)
+  )
+  (fp_line (start -21.75 0) (end 21.75 0)
+    (stroke (width 0.12) (type default)) (layer "Cmts.User") (tstamp 76dc068c-af65-429c-a9b4-838bdec183a1))
+  (model "${KIPRJMOD}/3Dmodels/Spacer2b.wrl"
+    (offset (xyz 0 66 4.5))
+    (scale (xyz 0.3937 0.3937 0.3937))
+    (rotate (xyz -90 0 0))
+  )
+)