Add automatic JWT parsing

[dutzi]

I have a branch where JWT are automatically parsed and viewed as JSON (instead of the base-64 string).

Here's how it looks like (note I'm going a step further and displaying the expiration date as readable date + "time until" pretty print).

Before:

After:

Would you like me to finalize it as a PR?

[warrenday]

Hey @dutzi thanks again for another PR. Could this on click of a checkbox/button?

It's a great idea, however not all users will want this by default.

Just to note: You can click the header directly to copy it, so we can't have the click to parse there.

[warrenday]

I've gone ahead and progressed with this one and added the parsing via double click. I'll close this issue for now, the feature will be in version 2.19.4.

Readme also updated with mouse and keyboard shortcuts.