[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/features/table/res/templates/historical-table.html

@@ -4,6 +4,6 @@
         rows="rows"
         enableFilter="true"
         enableSort="true"
-        class="t-tabular t-historical">
+        class="tabular-holder t-exportable">
     </mct-table>
 </div>

platform/features/table/res/templates/rt-table.html

@@ -4,6 +4,7 @@
         rows="rows"
         enableFilter="true"
         enableSort="true"
+        class="tabular-holder t-exportable"
         auto-scroll="autoScroll">
     </mct-table>
 </div>