rotate the entire viewer widget

* NOTE: currently this is hardcoded to 45 degrees for all viewers.  This will need to be controlled by some state object... but we don't have access to the viewer state at this level, so will likely need to be a per-viewer dictionary in the app state that is then controlled from a plugin in the UI.
* see notes about black background color

jdaviz/container.vue

@@ -53,8 +53,10 @@
 
         </div>
 
+        <!-- TODO: add background-color: black to v-card once also in canvas object -->
         <v-card tile flat style="flex: 1; margin-top: -2px; overflow-y: auto;">
-          <jupyter-widget :widget="viewer.widget" style="width: 100%; height: 100%"></jupyter-widget>
+          <jupyter-widget :widget="viewer.widget" :style="'width: 100%; height: 100%; transform: rotate('+'45'+'deg)'"></jupyter-widget>
+          <!-- child canvas object also needs background-color: black... possibly an upstream change to glue to have axes/viewer background colors alongside show_axes -->
         </v-card>
     </gl-component>
   </component>