Feature: opt-in survey when exiting a game

On first start-up, the game will ask if you want to participate
in our automated survey. You have to opt-in, and can easily opt-out
(via the Options) at any time.

When opt-in, whenever you exit a game, a JSON blob will be send
to the survey server hosted by OpenTTD. This JSON blob contains
information that gives a global picture of the game just played:
- What settings were used
- How many humans vs AIs
- How long the game has been played
- Basic information about the OS / CPU

All this information is kept very generic, so there is no
chance we send private information to our survey server.
Nothing in the JSON blob could identify you as a person; it
mostly tells about the game played. At any time you can see
what the JSON blob includes, by pressing the "Preview Survey
Results" button in-game.

src/crashlog.cpp

@@ -23,6 +23,7 @@
 #include "screenshot.h"
 #include "gfx_func.h"
 #include "network/network.h"
+#include "network/network_survey.h"
 #include "language.h"
 #include "fontcache.h"
 #include "news_gui.h"
@@ -511,6 +512,10 @@ bool CrashLog::MakeCrashLog() const
 		printf("Writing crash screenshot failed.\n\n");
 	}
 
+	if (_game_mode == GM_NORMAL) {
+		_survey.Transmit(NetworkSurveyHandler::Reason::CRASH, true);
+	}
+
 	return ret;
 }