Create composite client bundles directly under target

The target/pkg subdirectory is most certainly historical and certainly not
a requirement anymore. This commit modifies the release-clients build target
to move all the OMERO.clients zip directly under target instead.

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Strip launch scripts out of all OSX bundles

Scripts are currently not working out-of-the box and will need refactoring if
we want to re-include them.

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Merge pull request #2737 from sbesson/pkg_removal

Create composite client bundles directly under target