[UP-3717] Initial code for adding session timeout dialog support.   The JS is not yet completed, but I think most of the basic backend work is good (except for universality).
[UP-3717] Add support for universality.  Switched to jquery-ui from bootstrap since bootstrap didn't work well in universality.   Misc code cleanups.
[UP-3717] Updates based on code review comments.  Remove move "magic" values from the code.
[UP-3717] Updates based on code review comments.  Added additional comment to portlet.xml and changed "extend my session" button text to "Yes, keep me signed in" which is hopefully a bit more user-friendly.
Merge pull request #392 from jhelmer-unicon/UP-3717_session_timeout

UP-3717 - Add client-side warning re session timeout

with opportunity to renew session.