memory (persistent, sqlite): better private values handling + new LazyPersistentBinaryDict: - merged private values method handling in sqlite, and added a keys arguments to get only some keys - LazyPersistentBinaryDict allow to get values in database only when they are needed, saving memory for big data

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