Live preview: the tool alone, the boolean only on OK, computed off the window thread (#1201)

The preview builds only the tool; the boolean runs once on OK, off the window thread, with a Computing label while it takes a while. Follow-up to #1020.

assets/locales/de.json

@@ -10,6 +10,7 @@
   "browser.precision": "Genauigkeit: {precision}",
   "browser.sketch_name": "Skizze {number}",
   "browser.units": "Einheiten: {units}",
+  "dialog.computing": "Wird berechnet… {seconds} s",
   "dialog.custom_axis": "↖ Eigene Achse",
   "dialog.edit_title": "{title} bearbeiten",
   "dialog.select": "↖ Auswählen",

assets/locales/en.json

@@ -286,6 +286,7 @@
   "cmd.view_list": "List Named Views",
   "cmd.view_rename": "Rename Named View",
   "cmd.view_save": "New Named View",
+  "dialog.computing": "Computing… {seconds} s",
   "dialog.custom_axis": "↖ Custom Axis",
   "dialog.edit_title": "EDIT {title}",
   "dialog.select": "↖ Select",

assets/locales/ja.json

@@ -286,6 +286,7 @@
   "cmd.view_list": "名前付きビューを一覧表示",
   "cmd.view_rename": "名前付きビューの名前を変更",
   "cmd.view_save": "新規名前付きビュー",
+  "dialog.computing": "計算中… {seconds} 秒",
   "dialog.custom_axis": "↖ カスタム軸",
   "dialog.edit_title": "{title}を編集",
   "dialog.select": "↖ 選択",

assets/locales/ko.json

@@ -10,6 +10,7 @@
   "browser.precision": "정밀도: {precision}",
   "browser.sketch_name": "스케치{number}",
   "browser.units": "단위: {units}",
+  "dialog.computing": "계산 중… {seconds}초",
   "dialog.custom_axis": "↖ 사용자 정의 축",
   "dialog.edit_title": "{title} 편집",
   "dialog.select": "↖ 선택",

assets/locales/zh.json

@@ -286,6 +286,7 @@
   "cmd.view_list": "列出命名视图",
   "cmd.view_rename": "重命名命名视图",
   "cmd.view_save": "新建命名视图",
+  "dialog.computing": "正在计算… {seconds} 秒",
   "dialog.custom_axis": "↖ 自定义轴",
   "dialog.edit_title": "编辑 {title}",
   "dialog.select": "↖ 选择",