CHOP-70. Deprecate the need for the EXPRESS_CLASSPATH variable.

Currently when specifying any third-party dependencies (job jar, dependency
jars etc) when running the express command, the user must set the
EXPRESS_CLASSPATH variable ahead of time. Now that variable is deprecated in
favor of a command line option (--libjars) where the user can specify a colon
separated list of dependency jars.

Reviewed by: robert, kiyan