[web] start a new message system based on id of message stored in session's data instead of using __message as today, which is problematic (allow message injection). Also we can have html in messages. Removed the __createdpath hack used to escape those limitation. The old system should still work though (and will probably for a while, though we should progressivly move to the new system where it's possible). Cleanup request paramaters handling on the way.

msgid ""
msgstr ""
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Generated-By: pygettext.py 1.5\n"
"Plural-Forms: nplurals=2; plural=(n > 1);\n"