Clean up some cruft

- Remove post-card.back, fixes #5
- Remove unused `.bowerrc` in starter dir
- Merge `core-icon-button` styles in finished dir, fixes Polymer/polymer#570

Author: Rob Dodson

finished/post-card.back

@@ -32,8 +32,6 @@
       position: absolute;
       top: 3px;
       right: 3px;
-    }
-    core-icon-button {
       fill: #636363;
     }
     :host([favorite]) core-icon-button {