Fixed JIRA ICE-9357 : ICE Renderers have thread unsafe instance field

git-svn-id: http://anonsvn.icesoft.org/repo/icefaces3/trunk/icefaces@36439 1de00972-ac04-4911-a46b-06793c8d78d9
ICE-9383 Modified ResourceRegistry to not create a new session when looking up resource holders into the session. Also, modified EnvUtils.createSessionOnPageLoad to create a new session (if one is missing) only during incoming GET requests.

git-svn-id: http://anonsvn.icesoft.org/repo/icefaces3/trunk/icefaces@36442 1de00972-ac04-4911-a46b-06793c8d78d9
ICE-9387 modified loading of preview.html to use the mapping function to access it via the right URL

git-svn-id: http://anonsvn.icesoft.org/repo/icefaces3/trunk/icefaces@36444 1de00972-ac04-4911-a46b-06793c8d78d9