ODT fix + new feature (full control over ODF object)

Hello,

Here is a new commit which fix a problem with ODT segments temporary folders (which prevent odt with dynamic images to be generated), and adds an optional $odfHandler parameter for users' substitution functions, which extends ODT substitution functions to pretty much do anything because users now have full control over the ODF object.

For example, this allows to generate dynamic images for every products lines on-the-fly, which is not possible otherwise (except by modifying either the ODF class or Dolibarr generation classes...).

This patch is clean, small, and retrocompatible (if you didn't specify $odfHandler, the substitution function still works from my own tests).