update beta content for TW290b1

HelloThere: update links to Classic and TW5
SiteSubtitle: simplify wording
SiteTitle: add "Classic" to main title
WhatsNew: full documentation of changes by issues/pullrequest #
added version compare for beta output

point to new beta.html in test folder (copy of beta.2.8.1.html)
added beta.2.9.0.html for future comparisons
update version for full build (281 vs 290)

copy index.2.8.1.html to index.html in test folder for future version
comparison with full 2.9.0 build (upcoming)
update version number for TW290 builds