Thin Extrude: walls of a set thickness along sketch curves (#721) (#991)

Thin Extrude builds walls of a set thickness along sketch curves, open chains and closed loops, with the wall centred, inside, outside or on both sides at two thicknesses. Saved under format 20 (thin on an Extrude); an extrude without thin saves as before. Closes #721.

assets/locales/ja.json

@@ -959,6 +959,14 @@
   "Line Spacing": "行間",
   "Path": "パス",
   "sketch_text.on_path": "文字はパスに沿います: 位置は曲線で決まります",
+  "Thin": "薄肉",
+  "Thin Extrude": "薄肉押し出し",
+  "Wall Location": "壁の位置",
+  "Wall Thickness": "壁の厚さ",
+  "Thickness Outside": "外側の厚さ",
+  "Inside": "内側",
+  "Outside": "外側",
+  "Profiles/Curves": "プロファイル/曲線",
   "cmd.material_properties_validate": "物理材料データを検証",
   "cmd.material_properties_directional": "方向別弾性率",
   "update.button": "アップデート",