Add a getEncryptedString method in the Configuration interface

Hi guys,

it would be really awesome if the Configuration could be created with a passphrase (another constructor which accepts a string, let's say 'mypassphrase') and then you also add a method in the interface (let's say getEncodedString('database.password')) so we could have encoded properties in our properties files. Internally the method just needs to delegate to jasypt's StandardPBEStringEncryptor for instance

 StandardPBEStringEncryptor encryptor = new StandardPBEStringEncryptor();
            encryptor.setPassword("mypassphrase");
encryptor.decrypt("database.password");

decrypt the value and then return the decrypted value. This will allow for more secure property files.