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/DisplayLayout.vue

@@ -66,81 +66,6 @@
 </div>
 </template>
 
-<style lang="scss">
-    @import "~styles/sass-base";
-
-    @mixin displayMarquee($c) {
-        > .c-frame-edit {
-            // All other frames
-            //@include test($c, 0.4);
-            display: block;
-        }
-        > .c-frame > .c-frame-edit {
-            // Line object frame
-            //@include test($c, 0.4);
-            display: block;
-        }
-    }
-
-    .l-layout {
-        @include abs();
-        display: flex;
-        flex-direction: column;
-        overflow: auto;
-
-        &__grid-holder {
-            display: none;
-        }
-
-        &__frame {
-            position: absolute;
-        }
-    }
-
-    .is-editing {
-        .l-shell__main-container {
-            &[s-selected],
-            &[s-selected-parent] {
-                // Display grid and allow edit marquee to display in main layout holder when editing
-                > .l-layout {
-                    background: $editUIGridColorBg;
-
-                    > [class*="__grid-holder"] {
-                        display: block;
-                    }
-                }
-            }
-        }
-
-        .l-layout__frame {
-            &[s-selected],
-            &[s-selected-parent] {
-                // Display grid and allow edit marquee to display in nested layouts when editing
-                > * > * > .l-layout {
-                    background: $editUIGridColorBg;
-                    box-shadow: inset $editUIGridColorFg 0 0 2px 1px;
-
-                    > [class*='grid-holder'] {
-                        display: block;
-                    }
-                }
-            }
-        }
-
-        /*********************** EDIT MARQUEE CONTROL */
-        *[s-selected-parent] {
-            > .l-layout {
-                // When main shell layout is the parent
-                @include displayMarquee(deeppink);
-            }
-            > * > * > * {
-                // When a sub-layout is the parent
-                @include displayMarquee(blue);
-            }
-        }
-    }
-</style>
-
 <script>
 import uuid from 'uuid';