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.

server/publications/users.js

@@ -0,0 +1,11 @@
+Meteor.publish('user-miniprofile', function(userId) {
+  check(userId, String);
+
+  return Users.find(userId, {
+    fields: {
+      'username': 1,
+      'profile.fullname': 1,
+      'profile.avatarUrl': 1,
+    },
+  });
+});