ignore unknown JSON fields when deserializing to a POJO

An external REST API can be extended and stay backwards compatible,
for example just be adding new fields in the JSON result.

The default mapper is configured so that a client using the
java Play JSON API can still consume the external REST API.
fix #2562 extract code samples
Move the default template imports to the build-link project. Other implementers of build link besides just SBT will want to use the same list of default template imports
Merge pull request #3669 from benmccann/template-imports

Move the default template imports to the build-link project
Merge pull request #3671 from martinpallmann/issue-2562

fix #2562 extract code samples
Merge pull request #3670 from yanns/tolerant-java-json-mapper

ignore unknown JSON fields when deserializing to a POJO