First cut at improved undo
Remove chat window docking
Update chat window to use new Frameless Dialog

The new dialog class needed to be updated to handle windows in different
positions and windows that don't delete on close.
Update username in chat to use correct line height
Update chat textbox to use correct line height
Update style of chat message links
Fix bug where multiple user/location popups appear
Merge remote-tracking branch 'upstream/master' into 19554-2
Fix issue with pref dialog disappearing

With the frameless dialog being updated to support different types of
window, the pref dialog was no longer able to rely on it to keep itself
open in certain cases.  The window flags were also updated to update
after a "browse" call rather than in the slot so that it would still
execute in the case of cancelled selection.
Update chat window to use vertical layout
Update style of chat messages
Add right margin to user list area in chat
Fix chat messages not being html escaped
Fix color and size of font in timestamp chat messages
Disallow rich text from being pasted into the chat area
Add Menu slot to open urls
Update ChatMessageArea to open urls via Menu::openUrl
Add hifi link handling in chat for usernames and locations
Update username/location match in chat to be more lenient
Add emoticons to chat