DB-HOT-500 QA-4568 Cannot submit a tokenized form in contribute mode right after content creation/deletion

This patch does two things :
- Fixes the URL generated by the tokenized form to detect if we're in a GWT servlet request context and modifies it to use the URLGenerator to generate a proper content URL
- Modifies the form action URLs in the page form creation and the blog to be "relatively absolute" because this was causing problems in contribute mode when the browser URL and the currently viewed page did not match. In general to be compatible with contribute mode we should always use "relatively absolute" URLs and never page relative URLs.