various fixes

Conflicts:
	bpm/bonita-core/bonita-process-engine/src/main/java/org/bonitasoft/engine/api/impl/PlatformAPIImpl.java
fix concurrent session access
Conflicts:
	services/bonita-session/bonita-session-api-impl/src/main/java/org/bonitasoft/engine/session/impl/SessionProviderImpl.java
make code more readable
refactor lock mechanism: outside of tx when appropriate & more
synchronized
clean sysout and so on
remove exception when setting session on session accessor and that there is already one, because of services tests and local tests...
avoid NPE
fix lock service synchronization on unlock and lock was causing deadlock
remove unused class
remove useless synchronized
remove useless synchronized
remove useless else statement