Change the board import layout from a popup to a full page

This commit also removes the “import a single Trello card” as we couldn’t figure
out some reasonable use case.

We also create a new publication on the server to provide the minimal user
profile informations required to display an avatar.

client/lib/popup.js

@@ -142,6 +142,11 @@ window.Popup = new class {
     }
   }
 
+  getOpenerComponent() {
+    const { openerElement } = Template.parentData(4);
+    return BlazeComponent.getComponentForElement(openerElement);
+  }
+
   // An utility fonction that returns the top element of the internal stack
   _getTopStack() {
     return this._stack[this._stack.length - 1];