Topic themes (#2187)

* Bringing over in-progress changes from topic-core-css

- Adds _espresso-constants.scss;
- Cleanup colors and naming;
- Remove conflict res leftover 'domainObject' in mct-tree.vue;
- Still WIP!

* Various

- Remove pushBack / pullForward functions;
- Fix c-input-inline, remove bg until hover;
- TODO: input bg colors
- Increased margin in main-pane;

* Themeing WIP

- Conductor markup: convert to buttons for accessibility;
- Conductor styles consolidated and changed for better theme support;

* Themeing WIP; significant rewrite of pane headers

- Pane headers restructured for better semantics and clarity;
- Espresso design refined and tightened;
- Grid Vue changes for better themeing support;
- TODO: fix mobile version, collapse icon is whack;

* Restored Number-type input styling for correct positioning of spinner
button;

* Themeing mods for click-icon styles

* Bring Snow theme into style parity with Espresso

- TODO: refine Snow colors;

* Mobile styling fixed

- Mobile menu icon significant fixes;
- Hover only applied to desktop;
- Reorg of mixins;

* Bring Snow theme constants into parity with Espresso

- Refined Snow styles;
- Fixed missing scroll and padding in tree;
- Pane collapse button now uses proper color;
- Item Grid view refinement;
- Cleaned up code;

* Color fixes

- Super-menu description;
- Conductor time buttons hover;
- Datepicker "in-month" items color;
- Espresso colorKeyFilter brightened;

src/plugins/timeConductor/ConductorTimeSystem.vue

@@ -22,11 +22,11 @@
 <template>
     <div class="c-ctrl-wrapper c-ctrl-wrapper--menus-up"
          v-if="selectedTimeSystem.name">
-        <div class="c-button--menu c-time-system-button"
+        <button class="c-button--menu c-time-system-button"
             :class="selectedTimeSystem.cssClass"
              @click="toggleMenu($event)">
             <span class="c-button__label">{{selectedTimeSystem.name}}</span>
-        </div>
+        </button>
         <div class="c-menu" v-if="showMenu">
             <ul>
                 <li @click="setTimeSystemFromView(timeSystem)"
@@ -40,20 +40,6 @@
     </div>
 </template>
 
-<style lang="scss">
-    @import "~styles/sass-base";
-
-    .is-realtime-mode {
-        .c-time-system-button {
-            background: $colorTimeBg;
-
-            &:hover {
-                background: $colorTimeHov;
-            }
-        }
-    }
-</style>
-
 <script>
 export default {
     inject: ['openmct', 'configuration'],