[Feature] API pane UX enhancements

Bunch of enhancements that can make working with APIs easier:
1. Enable shift+tab for navigating backwards on key-value pairs
2. Enable creating new key-value pair with tab after existing ones are occupied
3. Reorder headers and params tab to include params first (need user research for this possibly, I'm more used to entering params first)
4. Enable converting headers and params into JSON object representation to copy it to and fro (From 3, I have written 10s of key-value pairs manually in one pane only to discover it belonged to the other pane and sadly had to do this by hand all over again, without tab assistance 😞)
5. Start with an empty key-value pair for multi part form data, like in headers and params