[Idea] Show .qxw and Fixture not present.

[lorenzoandreani]

A small improvement to simplify transfer show files between different computers.

Opening a file show .qxw and the fixture is not in the computer QLC+ signals (rightly) an error indicating that the fixture is not present.

It would be so convenient that QLC+ checks whether the folder of the show file if there is a file with the fixture and proposed to add the computer.

.....hopefully it might be useful a function to update the fixtures file on computer with those in the folder of the show.... checking dates and warning the user of a possible update of the fixture file.