Show Time Remaining when progress_bar utilised

[JackMcKew]

Hello!

I absolutely love this package, thank you so much!

One thing that I've found myself doing across projects using gooey is making an interface between Gooey and tqdm.

So I decided I'd make it inbuilt into Gooey! I've already created the feature along with tests and such, so this issue is a formality to ensure compliance with the contributing guidelines. Find the branch at: https://github.com/JackMcKew/Gooey/tree/1.0.4-release-tqdm-loading-bar, I will create a PR just after this issue is submitted.

The implementation is a Python 2.7 and 3 compatible 'extract' of the functionality in TQDM for Gooey

Furthemore, I've created a working example to add to the examples repository as well!

[chriskiehl]

Closing this since we merged in your feature : )