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/zh.json

@@ -959,6 +959,14 @@
   "sketch_text.on_path": "文字沿路径排列：由曲线放置",
   "ui.analysis": "分析",
   "ui.edit_section_analysis": "编辑截面分析",
+  "Thin": "薄壁",
+  "Thin Extrude": "薄壁拉伸",
+  "Wall Location": "壁位置",
+  "Wall Thickness": "壁厚度",
+  "Thickness Outside": "外侧厚度",
+  "Inside": "内侧",
+  "Outside": "外侧",
+  "Profiles/Curves": "轮廓/曲线",
   "cmd.material_properties_validate": "验证物理材料数据",
   "cmd.material_properties_directional": "方向弹性模量",
   "update.button": "更新",