Enhance ValueReader impl. to consider the JSON field type

This fine-tunes the conversion as one can tell whether the source is a
number of String, which makes a difference for dates for example.
Additionally, where possible the underlying JSON parser is used to
perform the conversion to leverage the JSON context.

Relates #271

(cherry picked from commit 8984fc3a28e1f0b55bdab9024710c82ee90e96ad)
Remove more compilation warnings

(cherry picked from commit a80086c8af9e65ff1a9f91815336bd5d393e745f)
Hive - Enhance integration test

Relates #271

(cherry picked from commit e230951296fdf121902877ecb6a3d98be9b85f59)
Hive-Update unit test mappings

(cherry picked from commit b8cf7098d17a359171ad5eb5fd59c8de106d1c6b)