Fixed Bug: inconsistent use of relative/absolute URLs

Some pages use relative links such as boards link at the home page.
 Others use absolute url such as cards in boards' lists.
 This commits goal is to allow for consistent use of relative
  urls.

Origin relative URLs also helps decoupling Wekan from the infrastructure
 it's deployed on. i.e if it's being served, it should work.

models/lists.js

@@ -280,6 +280,10 @@ Lists.helpers({
     const card = Cards.findOne({ listId: this._id });
     return card && card.absoluteUrl();
   },
+  originRelativeUrl() {
+    const card = Cards.findOne({ listId: this._id });
+    return card && card.originRelativeUrl();
+  },
   remove() {
     Lists.remove({ _id: this._id });
   },