core (tools/common): template renderer first draft: jinja integration is being rewritten to be used not only in Libervia, this is a first step which put the renderer in backend/frontends tools. The renderer is mainly HTML oriented, but may be used for other files. sat_templates dependency is needed to use it.

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