Fix eventData size limit of 255 bytes

* Overflow could be easily triggered by sending a long message
via the message center

Strip NULL when writing messages to file

* For original and binary recording engines
* This allows the messages file to be viewed in a text editor

Pulsepal setinterpulse fix

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