[Frontend] Styling Export button

fixes #973
- Done;
- Styling for Export button and tabular view
area in layout frame context;
- Export button in frame context now
hidden until user hovers over tabular
view area in frame, includes animated
transition;
- Normalized line-height on button and
menu elements in frame context;
- Layout/markup/SASS for historical and
RT tabular view modified;
- Converted imagery.html layout
to use flexbox;

platform/commonUI/general/res/sass/lists/_tabular.scss

@@ -24,6 +24,10 @@
 	height: 100%;
 }
 
+.tabular-holder {
+    @include absPosDefault();
+}
+
 .tabular,
 table {
 	box-sizing: border-box;
@@ -165,11 +169,38 @@ table {
 }
 
 /********************************************************** SPECIFIC TABULAR VIEWS */
-.t-tabular {
-    &.t-historical {
+.tabular-holder {
+    &.t-exportable {
         $btnExportH: 25px;
         .l-view-section {
             top: $btnExportH + $interiorMargin;
         }
     }
+}
+
+.child-frame {
+    .tabular-holder {
+        &.t-exportable {
+            $btnExportH: $btnFrameH;
+            .s-btn.t-export {
+                @include trans-prop-nice(opacity, $dur: 50ms);
+                opacity: 0;
+            }
+            .l-view-section {
+                @include trans-prop-nice(top, $dur: 150ms, $delay: 50ms);
+                top: 0;
+            }
+            &:hover {
+                .s-btn.t-export {
+                    @include trans-prop-nice(opacity, 150ms, 100ms);
+                    opacity: 1;
+                }
+                .l-view-section {
+                    @include trans-prop-nice(top, $dur: 150ms);
+                    top: $btnExportH + $interiorMargin;
+                }
+            }
+        }
+    }
+
 }