Atum model's serialization missing dependencies

[dk1844]

Thanks to a jointed effort with @Zejnilovic, it has been found out that Atum's model library needs the following dependencies to be present when running in a minimal project:

"org.json4s" %% "json4s-core" % "3.5.3" % Compile,
"org.json4s" %% "json4s-jackson" % "3.5.3" % Compile,

(json4s current version, will be normalized with rest of the project)

(Current test flow always included spark-related tests that happen to supply these libraries). However, atum-model should be usable as-is. If encouraging this problem until the fix is released, including these dependencies explicitly works as a workaround.