Properly read/write game result from/to .sgf files

[herzbube]

Currently if the app enters scoring mode and the user performs all the steps necessary to calculate a proper score, that score is forgotten as soon as the app leaves scoring mode.

Instead the score should somehow be stored in one of the Go classes (GoGame?) when the app leaves scoring mode. From there it can then be written to .sgf.

Conversely, when an .sgf is read, if an SGFCGameResult is available its information should be evaluated and stored in one of the Go classes (GoGame?).

[herzbube]

Some thoughts

• GoGameHasEndedReason may need to be adjusted. See SgfUtilities::gameResultForGoGameHasEndedReason().
• How to apply already existing scoring information when the app enters scoring mode?