fix(editor) fix css layout for safari

Due to editor layout implementation using flexbox, some fine tuning needed to be done for safari

Closes [BS-16105](https://bonitasoft.atlassian.net/browse/BS-16105)

frontend/app/js/editor/editor.less

 .content-wrapper {
   position: relative;
-  overflow: hidden;
+  overflow-x: hidden;
   flex: 1;
   display: flex;
   flex-direction: row;

frontend/app/js/editor/properties-panel/properties-panel.less

@@ -49,7 +49,8 @@
   background-color: @color-properties-bg;
   color: @color-properties-text;
   height: 100%;
-  position: relative;
+  width: 100%;
+  position: absolute;
 
   .help-block {
     color: @color-properties-help;
@@ -93,7 +94,6 @@
   padding: 0 1em;
   line-height: 1.5em;
   text-align: center;
-  min-width: @property-panel-min-width;
 }
 
 .PropertyPanel-PropertyIcon {
@@ -189,4 +189,4 @@ widget-property-field ul[typeahead-popup] {
   span {
     display: none;
   }
-}
\ No newline at end of file
+}

frontend/app/less/palette.less

 .Palette {
   width: @sidebar-palette-width;
-  height: 100%;
   transition: width @sidebar-transition;
   background-color: @color-palette-item-bg;
 
@@ -19,7 +18,6 @@
 .Palette-sections {
   background-color: @color-palette-bg;
   width: @sidebar-palette-section-width;
-  height: 100%;
 }
 
 .Palette-section {
@@ -53,9 +51,8 @@
 
 
 .Palette-widgets {
-  width: @sidebar-palette-width - @sidebar-palette-section-width;
-  height: 100%;
-  overflow-y: scroll;
+  flex: 1;
+  overflow-y: auto;
   border-right: 1px solid @color-palette-bg;
   border-top: 1px solid @color-palette-bg;
   background: