Run command line arguments in active instance instead of silently throw them away.

Run command line arguments in active instance instead of silently throw them away if an instance of an app is already running.

Example:

You have a Scratch instance, if you open you terminal and write:

$ scratch-text-editor ~/my_file.txt

It should open a new tab in a running instance of scratch, instead of simply exit.
In the case of scratch, in only needs to process the command_line method.