Add grab command to collect script's dependencies

Previously, run --local could be used to collect a script's
dependencies in ./repository. However, with this mechanism it wasn't
possible to collect the dependencies without running the application.

This commit adds a new command, grab, that can be used to collect
a script's dependencies in ./repository without having to run it.
run is configured with ./repository as a location in which it can find
its dependencies so that the previously collected dependencies
can be used when subsequently running the app.

As part of this work RunCommand and TestCommand have been refactored
to use common code for their common options:

	--no-guess-imports
	--no-guess-dependencies
	--classpath

Previously, the declaration and handling of the options was duplicated
in the two classes. GrabCommand also has these three options and uses
the same common code.