- Common interface for database driver added
- Database driver for cassandra is implemented as a singleton class

	modified:   .gitignore
	modified:   bin/cassandra_driver_test
	modified:   obj/cassandra_db.o
	modified:   obj/cassandra_driver_test.o
	modified:   src/database/cassandra_db.h
	modified:   src/interfaces/database_driver.h
	modified:   src/test/cassandra_driver_test.cpp