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/utility/file/FileManager.cpp

@@ -63,7 +63,7 @@ std::set<FilePath> FileManager::getAllSourceFilePathsRelative(const FilePath& ba
 	{
 		if (baseDirectory.exists())
 		{
-			absolutePaths.insert(path.relativeTo(baseDirectory));
+			absolutePaths.insert(path.getRelativeTo(baseDirectory));
 		}
 		else
 		{
@@ -78,7 +78,7 @@ std::vector<FilePath> FileManager::makeCanonical(const std::vector<FilePath>& fi
 	std::vector<FilePath> ret;
 	for (const FilePath& filePath: filePaths)
 	{
-		ret.push_back(filePath.canonical());
+		ret.push_back(filePath.getCanonical());
 	}
 	return ret;
 }