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/LicenseChecker.cpp

@@ -83,7 +83,7 @@ LicenseChecker::LicenseState LicenseChecker::checkCurrentLicense() const
 		return LICENSE_EMPTY;
 	}
 
-	if (!License::checkLocation(FilePath(appPath).absolute().str(), licenseCheck))
+	if (!License::checkLocation(FilePath(appPath).makeAbsolute().str(), licenseCheck))
 	{
 		return LICENSE_MOVED;
 	}