XNAT-4325: Added an Admin UI panel for setting site-wide alerts. Also optimized appearance and positioning of site-wide alerts and the warning bar.

XNAT-3846: disable login from IE 8 and show error message prompting usage of a newer browser; normalized property names in spawner.js; other minor JS tweaks to fix things IE was choking on.

Updated jQuery 1.x and jQuery migrate scripts; removed jQuery 2.x files since they weren't used; changed name of 'chosen' menu functions to a more generic name for future transition to another menu widget.

XNAT-4249: '...timed out...' message won't display on login page unless user's last session was terminated due to inactivity. Spawner changes: for 'href', 'src', and 'action' properties, values starting with */ will ensure the path starts at the site root; also added 'name' attribute to form panels.

XNAT-4219: switched to <button> element with appropriate class names. (please use <button> elements for buttons - use type="submit" if it's a submit button)

XNAT-3910, XNAT-3918, XNAT-4030: MAJOR UI CHANGES! NEW topBar nav menu and user bar; many, many tweaks to styling; removed a bunch of <table> elements that were used for layout; tweaked CSS to account for that; updates to 3rd-party JavaScript libraries (but rolled back jQuery to 1.12.0).

integrate gradle-xnat-plugin and work out configuration for Cargo deploy
tasks.