Add Pathfinding UI from v3

Added libpathing to LLPHYSICSEXTENSIONS_INCLUDE_DIRS
llviewermenu updated a bit to be closer to v-d/rlva. Best viewed without space changes.
Updated llresmgr.cpp from v-d to "handle special case of input value being zero"
pipeline update: hideObject, restoreHiddenObject, hideDrawable, and unhideDrawable added.

Thanks to Henri Beauchamp for some UI code touchups, thanks to Zi Ree for Rebake notification.
Thanks to Mobius Ryba and Ansariel Hiller for the V1-style pathfinding icons.

Note: When opening from pie menu object selection is lost, unless the floater is already open..
This provides a more reliable reproduction of the bug we've been having with inspect.

indra/llui/llresmgr.cpp

@@ -383,6 +383,13 @@ std::string LLResMgr::getMonetaryString( S32 input ) const
 
 void LLResMgr::getIntegerString( std::string& output, S32 input ) const
 {
+	// handle special case of input value being zero
+	if (input == 0)
+	{
+		output = "0";
+		return;
+	}
+
 	S32 fraction = 0;
 	std::string fraction_string;
 	S32 remaining_count = input;