Added a common database backend implementation.

Added sqlite (proof of concept)

persistence/implementation/common/database/database_config.e

@@ -0,0 +1,29 @@
+note
+	description: "Database configuration"
+	date: "$Date: 2014-08-20 15:21:15 -0300 (mi., 20 ago. 2014) $"
+	revision: "$Revision: 95678 $"
+
+deferred class
+	DATABASE_CONFIG
+
+feature -- Database access
+
+	hostname: STRING = ""
+			-- Database hostname.
+
+	username: STRING = ""
+			-- Database username.
+
+	password: STRING = ""
+			-- Database password.
+
+	database_name: STRING = "EiffelDB"
+			-- Database name.
+
+	is_keep_connection: BOOLEAN
+			-- Keep Connection to database?
+		do
+			Result := True
+		end
+
+end