src: implemented move constructor/assignment for filepath

* improves indexing performance by roughly 5%
* switched to use uniqu_ptr for boost path to get rid of including boost in header
* added different methods to change the current FilePath or to make a copy and change that one
* used these methods appropriately throughout the code base
* removed exists() method from FileSystem because it is already contained in FilePath
* added const in some places

src/lib/component/view/GraphViewStyle.cpp

@@ -486,7 +486,7 @@ GraphViewStyle::NodeStyle GraphViewStyle::getStyleOfBundleNode(bool isFocused)
 	return getStyleForNodeType(
 		NodeType::STYLE_BIG_NODE,
 		"bundle",
-		ResourcePaths::getGuiPath().concat(FilePath("graph_view/images/bundle.png")),
+		ResourcePaths::getGuiPath().concatenate(FilePath("graph_view/images/bundle.png")),
 		true,
 		false,
 		isFocused,