Added support to add properties to generated Maven pom

[lefou]

Also added a packaging attribute to PomSettings.

[lolgab]

LGTM! 👍
About the version scheme I was defining in the other PR, how does it play together with publishProperties?

[lefou]

@lolgab I'm a bit unsure what the better approach for versionScheme is. We can have a dedicated def versionScheme as you did in #1629 and derive the publishProperties from it, or we can provide some kind of constants to be used in publishProperties directly. Something like:

object VersionScheme {
  val Strict = ("info.versionScheme", "strict")
  ...
}

def publishProperties = Map(VersionScheme.Strict)

I like the former approach more.

I still struggle to find information if and how these properties are supported in ivy.xml.