Update styles for shadow dom

- Create a shared style module that is included in every custom element
- Add the shared style module to each existing element

Change-Id: I1ee382955afe4ff630548a6640e7c4d03688849d

polygerrit-ui/app/elements/admin/gr-admin-project-list/gr-admin-project-list.html

@@ -21,10 +21,12 @@ limitations under the License.
 <link rel="import" href="../../shared/gr-rest-api-interface/gr-rest-api-interface.html">
 
 <link rel="import" href="../../../styles/gr-form-styles.html">
+<link rel="import" href="../../../styles/shared-styles.html">
+
 
 <dom-module id="gr-admin-project-list">
   <template>
-    <style>
+    <style include="shared-styles">
       :host {
         display: flex;
         flex-direction: column;