Adds llfloaterdestinations.* and floater_destinations.xml (needs translations, but not really)
Adds GenericErrorPageURL, DestinationGuideURL (not persistent), DestinationGuideShown, and DestinationGuideRect to debug settings
Removes ShowcaseURLDefault in favor of DestinationGuideURL from upstream.
Also Adds ToolbarVisibleDestinations for the toolbar button, but I'll need to set up a nice way to make the button invisible when the url is empty before adding it to the gui... maybe.. or maybe it's just not important.
This commit comes with support for dynamically changing destination guide page based on opensimextras simulator features cap
