Sets the portlet mode of a portlet to the given portlet mode.
Possible values are the standard portlet modes and any custom portlet
modes supported by the portal and the portlet. Portlets must declare in
the deployment descriptor the portlet modes they support for each markup
type. Standard portlet modes are:
Not more than one portlet mode can be set.
If more than one portlet mode is set, only the last one set
is valid.
Note: The portlet may still be called in a different portlet mode in the
next render call, depending on the portlet container / portal.