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/telemetry-view.scss

@@ -0,0 +1,29 @@
+.c-telemetry-view {
+    display: flex;
+    align-items: stretch;
+
+    > * {
+        // Label and value holders
+        flex: 1 1 auto;
+        display: flex;
+        flex-direction: row;
+       // justify-content: center;
+        align-items: center;
+        overflow: hidden;
+        padding: $interiorMargin;
+
+        > * {
+            // Text elements
+            @include ellipsize();
+        }
+    }
+
+    > * + * {
+        margin-left: $interiorMargin;
+    }
+
+    .c-frame & {
+        @include abs();
+        border: 1px solid transparent;
+    }
+}