POM: bump to pom-imagej 2.51

This updates to scijava-common 2.33.0, with some needed bug-fixes.
ScriptGenerator: generate scripts in menu order

Rather than iterating over all modules from the module service directly,
we now use the menu structure obtained from the menu service. This
approach gives us the menus ordered by weight, so that we can write out
the script files in that same order, by prepending the file names with
the Unicode 0xfeff character ("ZERO WIDTH NO-BREAK SPACE").
Add unit tests for ScriptGenerator

In particular, this tests that the scripts are generated in the expected
directory structure, with the correct number of prepended 0xfeff Unicode
characters, so that they will be sorted properly in the OMERO menus.
Merge branch 'module-order'

Closes #21.