MATLAB toolbox: package and release fixes

This PR provides several fixes to the MATLAB toolbox in preparation of 5.0.0:
- updates `bfCheckJavaPath` to support the new `bioformats_package.jar` JAR file
- updates the MATLAB test suite to support the new JAR
- decreases the memory threshold in `bfCheckJavaMemory()` as suggested in #856
- modifies the `dist-matlab` target to bundle the Bio-Formats JAR within the toolbox zip under a prefix

To test this PR:
- make sure all the Bio-Formats tests are passing
- test the full toolbox installation workflow:
   - download `bfmatlab.zip` from the CI job, 
   - extract it on your local disk: all M files and bioformats_package should be under a folder called    `bfmatlab` 
    - start MATLAB and add this folder to tour MATLAB path 
    - open an image using `data = bfopen(…)`

/cc @pwalczysko @hflynn