JasyptPropertiesParser: Use interface for encryptor, remove getters

As discussed in https://github.com/apache/camel/pull/357.

Interface StringEncryptor provides encrypt and decrypt methods. Change property encryptor to interface instead of implementation, which is better for use with OSGI services.

I also propose to remove getters getEncryptor(), getPassword() and getAlgorithm(). As providing these internals should be unnecessary, and might be considered a security risk.