Refactor project/Build.scala. Fix compiler warnings

With build.sbt file this library may be simply used in multi-modules sbt project.
For example:
```scala
 lazy val root = Project(id = "root", base = file(".")) aggregate(core, ...)

  lazy val core = Project(
    id = "core",
    base = file("core"),
    ...
  ) dependsOn(eventsourced)

  lazy val eventsourced = Project(id = "eventsourced", base = file("libs/eventsourced"))
```