Shown unknown game variant message in GUI

[criezy]

Currently when an unknown game variant is detected, it adds a message in the log file and stdout so that the user can easily copy it to the clipboard and report the unknown variant. However this makes the message difficult to notice on some platforms. I think it should also be shown in the GUI in a dialog. And to make it easy to report the unknown game variant, this dialog could have, depending on the features available for the current platform:

• A button to copy the message to the clipboard.
• A button to open the bug tracker and pre-fill the description.

We already have an API to open a URL in OSystem, but the copy to clipboard is currently missing (we have only a paste from clipboard) and would need to be added.

[criezy]

To clarify, the message I am thinking of here is the one in AdvancedMetaEngine::reportUnknown() in engines/advancedDetector.cpp. There is also a very similar message in ScummMetaEngine::createInstance() in engines/scumm/detection.cpp.

[rootfather]

Currently working on the dialog and clipboard part. First results may follow tomorrow.

[criezy]

rootfather: I actually started working on that yesterday and implemented the clipboard part but haven't looked at the dialog at all, so you are welcome to work on this (otherwise I was planning to have a look next week-end).

I just pushed the clipboard commits to my fork in case you want to reuse them:
​https://github.com/scummvm/scummvm/compare/master...criezy:unknown-game-dialog

[rootfather]

criezy: Your implementation is far ahead of what I achieved so far, you implemented the clipboard part in a much nicer way than I did. I don't know if it makes sense to work on the dialog part or better leave this to you too...

[criezy]

rootfather: it's really up to you. If you want to work on this dialog, this could be a relatively easy task to get some more coding experience, and I will be happy to help you or give you feedback if needed. On the other hand if you prefer me to do it, I can work on it this weekend as I initially planned.

[rootfather]

criezy: Thanks for offering me help and feedback, I really appreciate it. I think I'll tackle this task then. Code will live at ​https://github.com/scummvm/scummvm/compare/master...rootfather:unknown-game-dialog.

[criezy]

The pull request from rootfather to add this dialog has now been merged.
Note that currently only the AdvancedMetaEngine uses this dialog. It would be good for other engines to also use it.