optional double submit prevention

duplicated post-requests shouldn't get processed

without jsf:
#1 post requests need to get synchronized (per session)
#2 post requests need to consume an existing request-token
#3 re-render the page in case of a duplicated post-requests (+ skip full processing)
#4 in case of jsf: reset the previous request-token(s) per window in case of a get-request (because a new page isn't aware of them)
#5 reset the request-tokens in case of a duplicated post-requests >per window<, since the page will get re-rendered with a new token
#6 don't create request-tokens in case of resource-requests
#7 ignore duplicated jsf-ajax requests (they shouldn't happen, since the jsf-js implementation has to process them sequentially)

with jsf2+ (and ds):
#1 ignore jsf-ajax requests since they have to be queued according to the spec.
#2 ignore get-requests since they >shouldn't< change the state (we couldn't support them at all)
#3 browser-window-handling is done implicitly (window-scoped bean)
-> only the handling of post-requests is needed