Add text diff tool

[yodigi7]

As part of roadmap updates.

Would be good to use the combo of these two libraries:
https://www.npmjs.com/package/diff
https://www.npmjs.com/package/diff2html

[yodigi7]

Did a little test separately from the tool. The diff2html by default produces the html under the Generate Diff button. It has the input file header which doesn't really apply to our case. Don't know if you care about that, could remove that header by stripping out parts of the generated HTML or should just leave it as is.

[yodigi7]

Not sure if you have any input @VikingLichens

[amwebexpert]

Not sure if you have any input @VikingLichens

Your suggestions seems to be aligned with the tools offered be this project!