[Fronted] Significant refactoring of mixins for containers and buttons

WTD-839
Refactoring in advance of style mods to switcher when in frame;
Cleanup of markup to remove 'icon' class from invoke-menu elements;

platform/features/plot/res/templates/plot.html

@@ -116,7 +116,7 @@
 
                         <span class="ui-symbol icon type-icon">{{plot.getMode().glyph}}</span>
                         <span>{{plot.getMode().name}}</span>
-                        <span class='ui-symbol icon invoke-menu'>v</span>
+                        <span class='ui-symbol invoke-menu'>v</span>
 
                         <div class="menu dropdown" ng-show="toggle.isActive()">
                             <ul>