Fix session timeout default value

Update DEFAULT_SESSION_TIMEOUT to use TimeUnit.MINUTES.toSeconds(30)
rather than TimeUnit.SECONDS.toMinutes(30) which would always return
0.

See gh-2084
Fix auto-configuration order for Spring Data Rest

Update Rest, Hypermedia and HttpMessageConverter auto-configuration to
ensure beans are created in the correct order.

Prior to this commit the MappingJackson2HttpMessageConverter bean would
not be created because Spring Data Rest's TypeConstrained versions had
already been registered.

Fixes gh-1729