Add hexadecimal editor for downlink enqueue'er

[JulianvDoorn]

• I have searched the issues of this repository and believe that this is not a duplicate.

Summary

In the image below it only three 'editors' are available for creating downlinks. Base64 and JSON. I think a hexadecimal editor would be really beneficial for developers of devices.

What is the use-case?

This might be helpful for device developers who might be interested into sending simple payloads. Typically these developers are pretty well versed in hex formats. For them it would be beneficial to be able to write payloads in hex instead of using base64 which is not designed to be written by hand at all.

Implementation description

I imagine that adding a tab HEX in the image below would be sufficient.

Can you implement this by yourself and make a pull request?

I'm personally not well versed in web development, so personally no.