Abstract the jquery-textcomplete integration with EscapeActions

We now can re-use this integration in multiple places, this will be
useful for #342 for instance.

client/lib/textComplete.js

@@ -0,0 +1,30 @@
+// We “inherit” the jquery-textcomplete plugin to integrate with our
+// EscapeActions system. You should always use `escapeableTextComplete` instead
+// of the vanilla `textcomplete`.
+let dropdownMenuIsOpened = false;
+
+$.fn.escapeableTextComplete = function(...args) {
+  this.textcomplete(...args);
+
+  // Since commit d474017 jquery-textComplete automatically closes a potential
+  // opened dropdown menu when the user press Escape. This behavior conflicts
+  // with our EscapeActions system, but it's too complicated and hacky to
+  // monkey-pach textComplete to disable it -- I tried. Instead we listen to
+  // 'open' and 'hide' events, and create a ghost escapeAction when the dropdown
+  // is opened (and rely on textComplete to execute the actual action).
+  this.on({
+    'textComplete:show'() {
+      dropdownMenuIsOpened = true;
+    },
+    'textComplete:hide'() {
+      Tracker.afterFlush(() => {
+        dropdownMenuIsOpened = false;
+      });
+    },
+  });
+};
+
+EscapeActions.register('textcomplete',
+  () => {},
+  () => dropdownMenuIsOpened
+);