tools (common/template): ScriptsHandler fix/improvments: ScriptsHandler was not used so far, this commit fix it to be usable: - script can be imported with "include" - generate_scripts is used to generate the <script> elements generation, in base page - paths use root_path, so they are adapted to context - generate_scripts return a Markup string, so it's not escaped

Use this module to temporary store files that need to be integrated to other
projects such as Wokkel.

For example, the changeset that introduced this folder adds RSM (XEP-0059)
support to Wokkel. The files in sat.tmp.wokkel are imported over the initial
wokkel files from sat.plugins.__init__.py