chore(index.html): update feature list

[skip ci]
chore($pre-release): switch to pre-release 4.2 code

[skip ci]
chore(*): Update staging branch for website to 4.2.0-6

Also point to S3 no-server live demo.

[skip ci]
chore(*): Remove line a bottom of demos

[skip ci]
feat($customize.html): Update form for 4.2.0 feats

Such as serverless S3 uploading and initial file list population.
Serverless S3 is only an option when the S3 endpoint is selected.

[skip ci]
fix($customize.html): Serverless option pos and UI

based on feedback:
Moved the serverless-s3 option into the "Optional Modules" section,
and made in unchecked by default.

[skip ci]
chore($release): prepare for 4.2.0 release
Merge branch 'site/4.2.0' into gh-pages

Conflicts:
	index.html