Prepare statistics for SQLite

Temporarily disable 30-day statistics for SQLite
https://github.com/marienfressinaud/FreshRSS/issues/100
https://github.com/marienfressinaud/FreshRSS/issues/90

app/Models/StatsDAOSQLite.php

@@ -0,0 +1,9 @@
+<?php
+
+class FreshRSS_StatsDAOSQLite extends FreshRSS_StatsDAO {
+
+	public function calculateEntryCount() {
+		return $this->convertToSerie(array());	//TODO: Implement 30-day statistics for SQLite
+	}
+
+}