interactive flag test to allow a script to check if it being run in an interactive session or in a batch operation from the jalview command line

Some scripted behaviour depends on if the script is run interactively by the user or if they have passed the script in via the command line. For example, test scripts would normally quit jalview after they have finished - but only if they were run non-interactively, otherwise, its more friendly to leave the Jalview instance running.