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/ui/preview/Preview.vue

@@ -54,37 +54,6 @@
     </div>
 </div>
 </template>
-<style lang="scss">
-    @import '~styles/sass-base';
-
-    .l-preview-window {
-        display: flex;
-        flex-direction: column;
-        position: absolute;
-        top: 0; right: 0; bottom: 0; left: 0;
-
-        > * + * {
-            margin-top: $interiorMargin;
-        }
-
-        &__object-name {
-            flex: 0 0 auto;
-        }
-
-        &__object-view {
-            background: $colorBodyBg;
-            border: 1px solid $colorInteriorBorder;
-            flex: 1 1 auto;
-            overflow: auto;
-            padding: $interiorMargin;
-
-            > div:not([class]) {
-                // Target an immediate child div without a class and make it display: contents
-                display: contents;
-            }
-        }
-    }
-</style>
 
 <script>
 import ContextMenuDropDown from '../../ui/components/contextMenuDropDown.vue';