Add Destination Guide

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

indra/newview/skins/default/xui/en-us/floater_destinations.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
+<floater
+ positioning="cascading"
+ legacy_header_height="225"
+ can_minimize="true"
+ can_close="true"
+ can_resize="true"
+ min_height="230"
+ min_width="350"
+ height="235"
+ layout="topleft"
+ name="Destinations"
+ single_instance="true"
+ help_topic="destinations"
+ rect_control="DestinationGuideRect"
+ control_name="DestinationGuideShown"
+ title="Destinations"
+ width="550">
+    <web_browser
+      bottom="-235"
+      height="215"
+      width="550"
+      follows="all"
+      name="destination_guide_contents"
+      trusted_content="true"/>
+</floater>

indra/newview/skins/default/xui/en-us/menu_viewer.xml

@@ -590,6 +590,11 @@
         <menu_item_call bottom="-29" height="19" label="Favorites" left="0" name="Favorites" width="166">
             <on_click function="ShowFloater" userdata="floater_inventory_favs.xml" />
         </menu_item_call>
+        <menu_item_check label="Destinations" name="Destinations">
+            <on_click function="ShowFloater" userdata="destinations"/>
+            <on_check function="FloaterVisible" userdata="destinations"/>
+            <on_visible function="World.VisibleDestinations"/>
+        </menu_item_check>
         <menu_item_separator bottom="-213" label="-----------" left="0" name="separator5"/>
 		<menu_item_call bottom="-251" enabled="true" height="19" label="My Land..." left="0"
 		     mouse_opaque="true" name="My Land..." width="185">

indra/newview/skins/default/xui/en-us/panel_toolbar.xml

@@ -287,6 +287,11 @@
         <button.commit_callback function="ShowFloater" parameter="teleport history"/>
       </button>
     </layout_panel>
+    <layout_panel name="paneldestinations" height="24" width="50" user_resize="false" visibility_control="ToolbarVisibleDestinations">
+      <button bottom="0" height="24" label="Destinations" name="destinations_btn" image_overlay="icn_toolbar_destinations.tga" image_overlay_alignment="left" image_selected="toolbar_btn_selected.tga" image_unselected="toolbar_btn_enabled.tga" image_disabled="toolbar_btn_disabled.tga" scale_image="true" width="50" follows="left|right">
+        <button.commit_callback function="ShowFloater" parameter="destinations"/>
+      </button>
+    </layout_panel>
     <layout_panel name="panel11" height="24" width="50" user_resize="false" visibility_control="ToolbarVisibleWorldMap">
       <button bottom="0" height="24" label="Map" name="map_btn" image_overlay="icn_toolbar_map.tga" image_overlay_alignment="left" image_selected="toolbar_btn_selected.tga" image_unselected="toolbar_btn_enabled.tga" image_disabled="toolbar_btn_disabled.tga" scale_image="true" tool_tip="Map of the world. (Ctrl-M)" width="50" follows="left|right" control_name="ShowWorldMap">
         <button.commit_callback function="ShowFloater" parameter="world map"/>