'Render and return the single page mako template that starts the app.
`app_name` (string): the first portion of the webpack bundle to as the app.
`entry_fn` (string): the name of the window-scope function that starts the
app. Defaults to \'app\'.
`bootstrapped_data` (dict): (optional) update containing any more data
the app may need.
`masthead` (boolean): (optional, default=True) include masthead elements in
the initial page dom.
`additional_options` (kwargs): update to the options sent to the app.'

def template(self, trans, app_name, entry_fn='app', options=None, bootstrapped_data=None, masthead=True, **additional_options):

    options = (options or self._get_js_options(trans))
    options.update(additional_options)
    return trans.fill_template(self.JS_APP_MAKO_FILEPATH, js_app_name=app_name, js_app_entry_fn=(entry_fn or self.DEFAULT_ENTRY_FN), options=options, bootstrapped=(bootstrapped_data or {}), masthead=masthead)
