[wsrp-interfaces] [wsrp][interfaces] Portlet mode/Window state types

In todays conference call we asked whether the current representation of
window states and portlet modes as bit vectors would adequately support
extensibility.  After a little discussion we tabled the question pending
information concerning how JSR 168 deals with this.

JSR 168 essentially represents these as Strings (wrapped by objects for
good OO).

I propose we do the same.
     -Mike-