[Fronted] Significant refactoring of btn classes

WTD-839
Refactoring in advance of style mods to switcher when in frame;
Moved btn styles from _controls.scss to _buttons.scss;
Markup cleaned up with css classing simplified;

platform/commonUI/browse/res/templates/create/create-button.html

@@ -21,7 +21,7 @@
 -->
 <div class="menu-element wrapper" ng-controller="ClickAwayController as createController">
     <div class="btn btn-menu create-btn major" ng-click="createController.toggle()">
-        <span class='ui-symbol major' href=''>+</span> Create<!--span class='ui-symbol invoke-menu'>v</span-->
+        <span class='ui-symbol' href=''>+</span> Create
     </div>
     <div class="menu dropdown super-menu" ng-show="createController.isActive()">
         <mct-representation mct-object="domainObject" key="'create-menu'">