Allow importing/exporting of test cases individually or by importing/exporting a tab

[houghtonap]

You can save the grammar to a file, but you are unable to save the test cases to a file(s).

What would be nice is to allow importing/exporting a tab in the playground as a zip file where the grammar and each individual test case is contained in the zip file. In addition, it would be nice to include a nodejs console app in the zip file that would require the grammar and take zero or more test dataset names on the command line, then it would produce a pass/fail for each test case, e.g., a simple test runner. Test datasets would be plain text files.

:+1: kudos for putting the playground together!!