[#101] Remove duplication in tests
[#101] Simplify Jackson HttpMessageConverter configuration
[#111] Ignore unknown field in JSON

New MappingJackson2HttpMessageConverter from Spring has that feature
disabled, so currently it just works (although in Jackson default
configuration that feature is enabled).
[#101] Make Jackson feature lists real constants

Due to a problem with constants in a trait they were converted into
an interface.
Merge pull request #122 from 4finance/topic/i101JacksonFeaturesB

Topic/i101 jackson features b