Convert RlvHandler to an LLSingleton for proper shutdown ordering, and shutdown RlvHandler before textures are destroyed to fix crash.

default many constructors and destructors

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  -> @accepttprequest will auto-accept all incoming teleport requests (allows exceptions - see @accepttp)
  -> @allowidle (stays experimental - subject to change)
  -> @getcommand:<filter> can be used to discover which commands are part of the user's RLVa implementation (with user-defined separator)
  -> @findfolders:<filter> works like @findfolder but will return all matches (with user-defined separator)
  -> @getdebug:<setting> can be used to query (but not set) the "RestrainedLoveforbidGiveToRLV", "RestrainedLoveNoSetEnv" and "WindLightUseAtmosShaders" debug settings
  -> @interact will block world interaction but allows drag-drop, the camera tool, mouse steering and access to the "self" context menu
  -> @sharedwear is the counterpart of @unsharedwear and wear locks the shared #RLV folder
  -> @sharedunwear is the counterpart of @unsharedunwear and remove locks the shared #RLV folder
  -> @touchhud will prevent the user from touching/clicking on their HUD attachments (allows exceptions)
  -> @tprequest will prevent the user from requesting teleports (allows exceptions - see @tplure)
  -> force wear commands will activate/deactivate gestures as well
  -> force wear commands will collect from folder links as well
  -> [FIXED] Location on incoming teleport requests isn't censored when @showloc restricted
  -> [FIXED] Message on outgoing teleport offers isn't censored when @startim restricted
  -> [FIXED] Message on outgoing teleport requests isn't censored when @sendim or @startim restricted

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- fixed : @setenv_preset:<name>=force and @setenv_daycycle:<name>=force don't change the current sky preset or day cycle

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    -> repro: execute a @setdebug_XXX/setenv_XXX:<option>=force command while another object already holds the @setdebug/setenv restriction
    -> eRet would remain at RLV_RET_UNKNOWN and trigger the "(fContinue) || (eRet != RLV_RET_UNKNOWN)" assertion

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- internal : the issuing object's UUID is stored in the RlvCommand so it no longer needs to be passed around as a separate parameter

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- internal : moved several rlvXXX helper and RlvHandler member functions into an RlvUtil helper class

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