[BUGFIX] Use same button rendering for morestep forms as it was done in jQuery version

the back button was rendered with btn-warning class before and should be displayed on the left.

Resolves: #757

Author: einpraegsam

Resources/Private/Partials/Form/Page.html

@@ -16,7 +16,7 @@
                 <button type="button" class="btn btn-primary pull-right" data-powermail-morestep-show="{iterationPages.cycle}">&gt;</button>
             </f:if>
             <f:if condition="!{iterationPages.isFirst}">
-                <button type="button" class="btn btn-primary pull-right" data-powermail-morestep-show="{iterationPages.index - 1}">&lt;</button>
+                <button type="button" class="btn btn-warning" data-powermail-morestep-show="{iterationPages.index - 1}">&lt;</button>
             </f:if>
         </div>
     </f:if>