Check for existence of faf-uid.exe

[muellni]

Warn the user if the required faf-uid.exe could not be loaded (like the runtime message did before). As a bonus, download the exe for the user.

[muellni]

Also create a test for the uniqueID() function for travis and appveyor.

[duk3luk3]

User may not have access to "Program Files (x86)" to download new faf-uid.exe, that needs to be checked first.

[duk3luk3]

This isn't critical and @muellni is busy with figuring out ICE, so I'm moving this to the "Next" milestone

[Wesmania]

Do we still want the faf-uid downloading functionality? If now, I can just make a small fix that will present the error info from stderr to the user.

[muellni]

The faf-uid and faf-ice-adapter downloading functionality would be nice if you run the client from source. We'd need a helpful error message with download instructions anyway. so let's just start with that.