Satisfy Issue 167: Ability to set global "add instead of wear" option in prefs

Adds debug setting LiruAddNotReplace.
Adds "Add clothing and wearables instead of replacing them" to Main (General) tab of Vanity Preferences.

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

@@ -7,6 +7,7 @@
       <check_box bottom_delta="-20" control_name="OptionPlayTpSound" follows="top" height="16" initial_value="true" label="Play the Teleport sound when moving between sims" tool_tip="Viewer will play the wooshing TP noise on teleport." name="tp_sound_check"/>
       <check_box bottom_delta="-20" control_name="AscentDisableLogoutScreens" follows="top" height="16" initial_value="true" label="Hide the Login/Logout progress screens" tool_tip="If checked, the viewer will hide the login/logout progress screen." name="disable_logout_screen_check"/>
       <check_box bottom_delta="-20" control_name="SGDisableChatAnimation" follows="top" height="16" initial_value="false" label="Disable chat, whisper and shout animations" tool_tip="Remove chat animations from your own avatar. Effect visible to everyone" name="disable_chat_animation"/>
+      <check_box bottom_delta="-20" control_name="LiruAddNotReplace" follows="top" height="16" label="Add clothing and wearables instead of replacing them" tool_tip="When double clicking or pressing enter in inventory with wearables or objects selected they will be added to your outfit, instead of replacing the wearable or object currently at their target destination." name="add_not_replace"/>
     </panel>
     <panel border="true" left="1" bottom="-190" height="180" width="500" label="Tags/Colors" name="TagsColors">
       <!-- Client tag options -->