Spring IO Platform already provides dependency management for JavaMail.
This commit updates Boot’s new JavaMail dependency management to align
with the Platform, thereby allowing the Platform to inherit Boot’s
dependency management instead of defining its own.
This commit adds a new starter to auto-configure a MailSender when the
necessary classes are present and when the property "spring.mail.host" is
set.
The auto-configuration also accepts any arbitrary properties that
JavaMail might need using the "spring.mail.properties" prefix.
Fixes gh-1760
Spring Buildmaster
Andy Wilkinson
Stephane Nicoll