Fixed concurrency issue and made REDIS configurable

This minor release includes fixed and minor features.

1. It fixes a concurrency issue within the scheduler.
2. Uses a new version of EmbeddedResids that shuts down the Thread pool executor on application close.
3. it adds the support for providing REDIS settings via the new application property
   spring.mail.scheduler.persistence.redis.settings. The provided properties must be comma separated. For instance: spring.mail.scheduler.persistence.redis.settings=appendfilename email_appendonly.aof, dir /Users/your_username/REDIS/AppendOnlyFiles