Remove .jsx from Javascript file extensions and create an jsx-mode

[petetnt]

This PR removes .jsx from Javascript file extensions and creates an separate jsx-mode.

[MiguelCastillo]

@petetnt we have used the convention in the past to put in the title of the PR "[DO NOT MERGE]" or something to that extent for a more visual cue of the status of the PR.

Correction. I think the convention was "[REVIEW ONLY]"... :)

[MiguelCastillo]

Looking forward to this :)

[petetnt]

@MiguelCastillo Yeah that's probably a good idea. I changed the title 👍

[MiguelCastillo]

I created and added a label to track PRs that shouldn't be merged. :) Easier to filter

[petetnt]

CodeMirror is now merged so this should be too. Ping @MiguelCastillo

[MiguelCastillo]

@petetnt Yup - this is my next item on the list :)

[marcelgerber]

I think this is an easy merge now. Is there something blocking this, @MiguelCastillo @petetnt?

[petetnt]

@marcelgerber nope AFAIK. Just needed the CodeMirror update. Cannot remove the do not merge tag myself but there shouldn't be anything to stop merging this, actually merging this would be really beneficial 💰

[MiguelCastillo]

Yeah you guys are right. I completely disappeared for a bit and neglected. Merging now.

[MiguelCastillo]

It works very nicely too! Thank you @petetnt.