DATAMONGO-764 - Added SSL support to Mongo configuration options.

Added support for allowing Mongo clients to use secure SSL connections by introducing the "ssl" property in MongoOptionsFactoryBean that will enable the use of the configured SSLSocketFactory to create SSLSockets. If no custom SSLSocketFactory is configured SSLSocketFactory#getDefault() will be used. We introduce this configuration in a new version of spring-mongo-1.4.xsd.

Applied Mike Saavedra's pull request (#75) with the above mentioned extensions.

Original pull request: #83.
DATAMONGO-764 - Polished JavaDoc in MongoOptionsFactoryBean.