PERF: styler uuid control and security
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

`Styler` uuid is randomly generated from 16bytes, or 128bit entropy, which is poorly formatted for data transmission over the web.
`Styler` uuid1 is super-ceded by uuid4 which is more network secure.

This PR addresses the two above items by switching uuid method, and then coding the default entropy to 5 characters (20bit) which should be more than sufficient to avoid HTML table collision on a webpage, but make substantial data transfer savings for large tables.

uuid length remains configurable. 
lgtm. @WillAyd if you have any remaining comments. Thanks @attack68 