Introduce a setting for Automatically scrolling to the bottom of a chat when the chat gains focus

Preferences->Adv. Chat->Chat UI, Autoscroll to the end of chats when they regain focus.
This defaults to false, unlike the legacy behavior.

Partial revert of "Feature Removal!: Do not scroll to the end of chats when the corresponding chatbar regains focus!"
Meeting Request: Change System Preferences' Security tab to Security & Privacy
Meeting Request: Display date not just time in Teleport History

Will not change old entries because of the stupid way teleport history is saved.
Seriously, this floater needs a rewrite... we should just use v3.
Meeting Request: Pick up LL's changes to land impact (Also introduces Land Impact floater)

Small change to lltextbox allowing us to use value attribute with <text/>'s YAY!!

Cleaned up in llfloatertools as well to better diff.