Reorganize: kebab-case names, per-item subdirectories, regroup items

v1/scad/objects/prusa-enclosure/mount-corner.scad

@@ -0,0 +1,3 @@
+use <../../lib/prusa_enclosure/mount.scad>
+
+prusa_enclosure_mount(angle=15);

v1/scad/objects/prusa-enclosure/washer.scad

@@ -0,0 +1,3 @@
+use <../../lib/prusa_enclosure/washer.scad>
+
+prusa_enclosure_mount_washer();