imagej-omero: move subroutines to the top
imagej-omero: use a more robust test for OMERO

We now look for blitz.jar, rather than only a directory called "lib".
imagej-omero: pass OMERO home as script argument

This is better than requiring OMERO_HOME to be set, since setting
OMERO_HOME has other (probably undesirable) ramifications.
imagej-omero: add TODO reminder about IMAGEJ_HOME
Rename imagej-omero to install-imagej

The script is migrating toward more of a focus on simply bootstrapping
an ImageJ installation with OMERO-5.0 update site enabled.
Make script generation script a shell script

Now that our ImageJ installation has everything included within it to
communicate with OMERO, we can generate scripts using a shell script
that simply invokes the ImageJ launcher with the script generator as
main class.
README.md: update to new installation instructions
install-imagej: make ImageJ folder configurable
ScriptGenerator: use base OMERO dir as arg

Previously, the script generator accepted the exact path (e.g.,
$OMERO_DIR/lib/scripts/imagej where OMERO script stubs were supposed
to go). But it makes more sense to accept the root directory of the
OMERO installation, verify that the argument is in fact valid, and
then generate the scripts in the appropriate subdirectory always.

With this change, the generator now exits with a non-zero error code
if something goes wrong.
WIP: how to make the installation better