Switched Scala version to 2.12.2, the most recent stable version.  It
will now require Java 1.8.

Fixed existing uses of deprecated features.

Removed the `uvm.clientsupport` package.  This package was intended to
help Mu clients build text-based Mu IR bundles.  However, we started
using the IR Builder API instead, and the `uvm.clientsupport` package
remained unused.  The same capability can be provided by the
`mu-tool-compiler` project
(https://gitlab.anu.edu.au/mu/mu-tool-compiler).  `uvm.clientsupport`
provided a non-SSA-to-ssa converter, which can be useful for clients.
If there are needs of resurrecting that feature, please checkout the
previous commit.