Added a common database backend implementation.

Added sqlite (proof of concept)

persistence/implementation/sqlite/scripts/tables.sql

@@ -0,0 +1,14 @@
+DROP TABLE IF EXISTS nodes;
+
+CREATE TABLE nodes
+(
+	id smallint unsigned NOT NULL auto_increment,
+	publication_date date NOT NULL,  #When the article was published
+	creation_date  date  NOT NULL, #When the article was created
+	modification_date  date  NOT NULL, #When the article was updated
+	title varchar(255) NOT NULL, #Full title of the article
+	summary text NOT NULL, #A short summary of the articule
+	content mediumtext NOT NULL,  #The HTML content of the article
+
+	PRIMARY KEY (ID)
+);