splitter constructor doesn't set processor type, with fun consequences

put MAC_PACKAGE_DIR/include on header search path for all plugins

add pre-build action to create Env.xcconfig if it doesn't exist

Fix audiomonitor offset

Xcode projects for OpenEphysHDF5Lib and NWBFormat

Added Xcode project for OpenEphysHDF5Lib, which builds a shared library (libOpenEphysHDF5.dylib) and installs it in open-ephys.app/Contents/Frameworks.  On macOS, the KWIKFormat plugin now links against libOpenEphysHDF5.dylib.

Added Xcode config files for building dylib's that are embedded in open-ephys.app/Contents/Frameworks

Symbol visibility fixes

Ensure that plugin entry points are always exported on macOS and Linux (otherwise, plugins won't load in macOS release builds)

Mac build updates

The Intan recording module allows users to route two channels to the
audio jack on the acquisition board. Up to this point, selecting channel
1 in the params tab would output software channel 2. In addition,
channel 1 is inaccessible.

This stems from a mismatch between the one-based indexing used by Open
Ephys GUI and the zero-based indexing that the Intan ecosystem uses.