Solution for login_block.xhtml: handle ajax exceptions

- ViewExpiredException is thrown when session timeouts
- the key is to catch the exceptions and render the entire page again
for partial requests by possibly setting
context.getPartialViewContext().setRenderAll(true)
(http://stackoverflow.com/questions/11203195/session-timeout-and-viewexpiredexception-handling-on-jsf-primefaces-ajax-request/11206114#11206114)