[Frontend] Refactor to use s-status-editing instead of ng-class

open #468
Remove ng-class statements in favor of upstream .s-status-editing;
Restructure CSS accordingly;
NOTE: because edit.html has NOT been changed,
changes here will cause old edit mode to no longer display properly.
Don't integrate this CSS with old edit mode!

platform/features/timeline/res/sass/_activities.scss

@@ -54,7 +54,8 @@
 	}
 }
 
-.edit-mode .s-timeline-gantt {
+.edit-mode .s-timeline-gantt,
+.s-status-editing .s-timeline-gantt {
 	.handle {
 		cursor: col-resize;
 		&.mid {

platform/features/timeline/res/sass/_timeline-thematic.scss

@@ -69,7 +69,8 @@
     }
 }
 
-.edit-mode .s-timeline-gantt {
+.edit-mode .s-timeline-gantt,
+.s-status-editing .s-timeline-gantt {
     .bar {
         &:hover {
             @include background-image(linear-gradient(lighten($colorGanttBarBg, 20), lighten($colorGanttBarBg, 10)));
@@ -140,7 +141,8 @@
     }
 }
 
-.edit-mode .s-swimlane {
+.edit-mode .s-swimlane,
+.s-status-editing .s-swimlane {
     cursor: pointer;
     .t-object-label {
         @include border-radius($controlCr);