[BEAM-3249] Only generate all artifacts when publishing.

[lukecwik]

This removes enableShadow since the user can now pass in the shading configuration closure explicitly.

Had to re-add propdeps-maven since it was supplying a task needed for uploadingArtifacts (which is part of the old 'maven' plugin). It seems like we are mixing stuff from the old 'maven' and the new 'maven-publish' tasks which requires further investigation.

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