Imagery fixes (#2668)

* Fix imagery-related styles and markup

- VERY WIP!!!
- Style modernizing;
- Also, padding fixes for pane.scss - unit test for regressions!

* Fix imagery-related styles and markup

- VERY WIP!!!
- Style modernizing WIP;
- Fixes to pane classes for better padding in vertical panes;

* Fix imagery-related styles and markup

- Migrated all imagery CSS into imagery-view-layout.scss from _legacy
.scss;
- CSS cleanups;
- Refactoring/simplification of thumb layout;
- Color fixed for $colorPausedFg in theme constants;

* Scroll to right instead of bottom, on autoscroll.

* Fix imagery-related styles and markup

- Make the most recent thumb visually distinct;
- Clicking a selected thumb now deselects it and unpauses the view;

* Imagery fixes

- Fixed thumb click logic to properly toggle paused when clicking a selected thumb;
- Improved CSS so that `selected` updates more quickly when selecting the latest thumb;
- Clicking the main image pause button now selects the proper thumb;

* Fix linting errors

Co-authored-by: Nikhil <nikhil.k.mandlik@nasa.gov>

src/ui/layout/pane.scss

@@ -62,6 +62,8 @@
     }
 
     &[class*="--horizontal"] {
+        padding-left: $interiorMargin;
+        padding-right: $interiorMargin;
         &.l-pane--collapsed {
             padding-left: 0 !important;
             padding-right: 0 !important;
@@ -69,9 +71,11 @@
     }
 
     &[class*="--vertical"] {
+        padding-top: $interiorMargin;
+        padding-bottom: $interiorMargin;
         &.l-pane--collapsed {
             padding-top: 0 !important;
-            padding-top: 0 !important;
+            padding-bottom: 0 !important;
         }
     }
 
@@ -277,6 +281,9 @@
             /************************** Vertical Splitter Before */
             // Pane collapses downward. Used by Elements pool in Inspector
             &[class*="-before"] {
+                $m: $interiorMarginLg;
+                margin-top: $m;
+                padding-top: $m;
                 > .l-pane__handle {
                     top: 0;
                     transform: translateY(floor($splitterHandleD / -1));