AMQP-432: Properly convert BasicProperties values to and from
MessageProperties

JIRA: https://jira.spring.io/browse/AMQP-432

Previously `DefaultMessagePropertiesConverter` converted just
`LongString`,
but BasicProperties may contain List and Map values with nested
LongStrings. Values unsupported by AMQP which are contained in Lists or
Maps are also not converted from `MessageProperties` to
`BasicProperties`.

Add logic to properly convert from LongString values nested in
Lists/Maps.
Add logic to properly convert unsupported values nested in Lists/Maps to
Strings.

**Cherry-pick to 1.3.x**

Code style polishing