Fix pagetemplate import for Plone 4.3 compatibility

``zope.app.pagetemplate.viewpagetemplatefile.ViewPageTemplateFile`` was moved to ``zope.browserpage.viewpagetemplatefile.ViewPageTemplateFile``

- ``zope.app.pagetemplate`` is no longer included in Plone >= 4.3
- ``zope.browserpage.viewpagetemplatefile`` works from Plone >= 4.1

btw. is ``Products.Five.browser.pagetemplatefile.ViewPageTemplateFile`` preferred?