This change means that imported juce modules will be made available both
with and without a namespace prefix, e.g. `juce_core` and
`juce::juce_core` will both be created.

This change allows custom modules to specify dependencies without a
juce:: prefix, which allows the modules to be used with the Projucer, or
under CMake with JUCE in a subdirectory, or under CMake with JUCE
installed to the system.

Building AudioUnits with an older CMAKE_OSX_DEPLOYMENT_TARGET
(e.g. 10.9) but a newer sdk (e.g. 10.15) would result in link
failures. Linking against the AudioUnit framework supplies the
missing symbols.

AudioUnits built with the Projucer also link CoreAudioKit, so
we do that in CMake too for consistency.

The module binary now has the extension `.so` instead of `.vst3`.

This change helps to avoid ambiguity in includes when building projects
which contain more than one "BinaryData.h".

Once JUCE has been built, you can use the following line to include
the targets from the build tree (replace `JUCE_BUILD_DIR` as
appropriate).
```
include("${JUCE_BUILD_DIR}/JUCEExportConfig.cmake")
```