INTSAMPLES-138: Make SI 4.1 as minimal

JIRA: https://jira.spring.io/browse/INTSAMPLES-138

* Upgrade to Boot 1.2, which is based on the SI 4.1
* Upgrade to SF 4.1.1
* Fix `feed` sample to use new `Rome` dep. from SI
* Fix deprecations for `@Payload`, `@Header` etc.
* Fix mongo` sample deprecation warn