Allows DV7toDV8.sh script to work on non-Mac hardware

[ajyey]

This MR allows the script to run on non-mac hardware.

My home media server runs on Linux and I do most of my work there, so being able to run this on Linux seemed like it would also be helpful for other users.

This MR:

• Adds support for additional command line arguments
• Updates the README to reflect those arguments
• Slightly rewords some things in the README
• Only prompts the user for language codes via applescript if the user is running on a Mac and they have not passed in the language codes via command line argument