Replace the component bounded cachedValue by a global UnsavedEdits

This new draft saving system is currently only implemented for the
card description and comment. We need better a component
inheritance/composition model to support this for all editable fields.

Fixes #186

server/publications/unsavedEdits.js

@@ -0,0 +1,5 @@
+Meteor.publish('unsaved-edits', function() {
+  return UnsavedEditCollection.find({
+    userId: this.userId
+  });
+});