[Tables] - Sticky headers (#2071)

* first revision

* [Frontend] Styling for sticky table headers

Fixes #1481
- WIP convert mct-table layout to use flex;
- TODO: fix flex layout when a small number of rows;
- Rename CSS classes used as selectors by JS;

* remove header height from calculations since it is outside in its own table now

* [Frontend] Styling for sticky table headers

Fixes #1481
- Fixed flex layout when a small number of rows;
- Refined input padding and dropshadow for more compactness;

* fix tests and verify tables works properly in layout and large view

* add mct-scroll to header table to allow scrolling in sync with the rest of mct-table

* Various fixes and polishing

Fixes #2071
- Fix headers height issue;
- Move inline styles to classes;
- First round fix for horz overflow due to scrollbar problem;

* WIP horz overflow

Fixes #2071
- Commented out CSS-based scrollbar with approach in
anticipation of better JS solution;

* Horz overflow/scrollbar problem fixed

Fixes #2071
- Added calcTableWidthPx to allow sizing-table to subtract
width of scrollbar;

* Remove commented code

* add clear icon back into filter text boxes

* Polishing on sticky table headers filtering

Fixes #1481
Fixes #2071
- Now hides the magnify glass in table header filters when typing;

platform/commonUI/general/res/sass/_global.scss

@@ -199,12 +199,18 @@ a.disabled {
 }
 
 .vscroll {
+    overflow-x: hidden;
     overflow-y: auto;
     &.scroll-pad {
         padding-right: $interiorMargin;
     }
 }
 
+.vscroll--persist {
+    overflow-x: hidden;
+    overflow-y: scroll;
+}
+
 .slidable {
     cursor: move; // Fallback
     cursor: grab;