Feature request: add tabs

**shawn.inder** ([Bug 60934](https://bz.apache.org/bugzilla//show_bug.cgi?id=60934&redirect=false)):
Image you're working on a test plan and a test fragment you use in that plan. To do this, you need 2 instances of JMeter opened. I've gotten quite used to using tabs for this sort of thing (that's how it works in my browser, in my editor, in my apps, etc.).

Would it be an option to add tabs to JMeter to allow working on multiple `.jmx` files within the same instance of JMeter?

OS: Linux