Choose installation path

**Problem/Reproduction:** When you launch the installer on Windows and click the _install_ button, the program will be installed directly into a predefined directory.

**Expected result/Solution:** On windows this behaviour is not expected, so there should at least be a warning, i.e. _The program will be installed to c:/whatever. Yes/No?_. The better way would be asking for user for choosing a directory (which can be set to a default value if the user does not choose one).