Scala : pave the way to migrate to Banana 0.7.1

- now use rw() and r() new transation API in Banana 0.7
- but still use JenaStore in some places
- temporarily add JenaDatasetStore.scala , Transactor.scala , copied from Banana
Notes: Tests: succeeded 7, failed 4 : because of transactions within transactions
Play! app is certainly broken
Migration to Banana 0.7.1-SNAPSHOT

Hope it's not a target moving too fast :)
Main points:
- new transaction API (formerly Banana API used to start transactions itself, now it's application only)
- JenaStore.scala has disappeared, replaced by JenaDatasetStore.scala; but now it's the application that holds the Jena Dataset(s)
- new generic parameter M for traits having function with results like SPARLQL : a wrapper ("context") for results, typically Try, but also Future for HTTP SPARQL
- some unclean stuff like isURI() has disappeared
TODO : add a transaction in StringSearchSPARQL, clean code, move the Jena dependencies in a modular part.
add a transaction in StringSearchSPARQL (FIXes the feature), clean code in FormSaver.scala; update tasks in README