Theming (#2567)

* Separate Vue component styles out from SFCs.
* Added 'MCT.prototype.getAssetPath' and using 'openmct.setAssetPath' to get relative path for assets.
* Re-implements `openmct.plugins.Snow()`, and `openmct.plugins.Espresso()` (as well as a new theme `openmct.plugins.Maelstron()`)

src/plugins/displayLayout/components/BoxView.vue

@@ -34,19 +34,6 @@
 </layout-frame>
 </template>
 
-<style lang="scss">
-    @import '~styles/sass-base';
-
-    .c-box-view {
-        display: flex;
-        align-items: stretch;
-
-        .c-frame & {
-            @include abs();
-        }
-    }
-</style>
-
 <script>
 import LayoutFrame from './LayoutFrame.vue'