Added a common database backend implementation.

Added sqlite (proof of concept)

persistence/implementation/common/string_helper.e

@@ -0,0 +1,53 @@
+note
+	description: "Summary description for {STRING_HELPER}."
+	date: "$Date: 2014-08-08 16:02:11 -0300 (vi., 08 ago. 2014) $"
+	revision: "$Revision: 95593 $"
+
+class
+	STRING_HELPER
+
+feature -- Access
+
+	is_blank (s: detachable READABLE_STRING_32): BOOLEAN
+		local
+			i,n: INTEGER
+		do
+			Result := True
+			if s /= Void then
+				from
+					i := 1
+					n := s.count
+				until
+					i > n or not Result
+				loop
+					Result := s[i].is_space
+					i := i + 1
+				end
+			end
+		end
+
+	indented_text (pre: READABLE_STRING_8; t: READABLE_STRING_8): READABLE_STRING_8
+			-- Indendted text.
+		local
+			s8: STRING_8
+		do
+			s8 := t.string
+			s8.prepend (pre)
+			s8.replace_substring_all ("%N", "%N" + pre)
+			Result := s8
+		end
+
+
+	json_encode (a_string: STRING): STRING
+			-- json encode `a_string'.
+		local
+			encode: SHARED_JSON_ENCODER
+		do
+			create encode
+			Result := encode.json_encoder.encoded_string (a_string)
+			debug
+				print ("%NResult" + Result)
+			end
+		end
+
+end