Integrate lupdate tool to generate *.ts files.

Currently, there is no support for lupdate tool with QBS tool. The *.ts files have to be created manually.

Conceptually, the lupdate tool is a bit different from a build system point of view, as it modifies a subset of its inputs (which somehow makes them source files and generated files at the same time). It would be great if anyone has spent time thinking about how to implement this in a clean and effective way.