Remove OpenTopo button; use first online map in mapconfig as default

[cyberang3l]

Removing the OpenTopo button was a bit more challenging that we thought, as when the map config is broken AviTab will fail to load any map. I came up with a solution that uses a hardcoded fallback map (OpenTopoMap) to get around this issue. The hardcoded fallback map will only be used when the config is broken. When the config is correct, the first enabled map that is found in the config is used as the default map. As a bonus, we now also support letting users choose their favorite default map by modifying the config. The feature in this commit commit work as follow:

• I added a new bool init flag in the MapApp::setMapSource function. The init flag is false by default, and the only time I set it to true is when calling the setMapSource function from the MapApp constructor.
• The MapApp::selectOnlineMaps function was also extended with two additional variables: One to hint if the function is called for interactive usage or not, and the second one passes a hardcoded fallback OnlineSlippySource (OpenTopoMap) that is used whenever we fail to read the mapconfig.json properly.
• When the setMapSource function is called with init == true, and the map source is MapSource::ONLINE_TILES, the selectOnlineMaps method is called in non-interactive mode.
• selectOnlineMaps in non-interactive mode will first try to parse the mapconfig.json. If that fails, it will show an error to the user (so now when the user messes up with the mapconfig.json, they will be notified to fix it right when they start AviTab), and set the default map to the hardcoded fallback map (OpenTopoMap). If the mapconfig.json can be parsed correctly, the first enabled map that is found in the config will be used as the default map. By default, with the config we ship in AviTab, the default map is OpenTopoMap. But if user wants to use a different default they can now do that by moving to the top of the mapconfig.json the map definition of their choosing.
• selectOnlineMaps in interactive mode will work as it used to: show up the menu if the mapconfig.json can be parsed correctly, and let the user pick their map. In the unlikely event that the map can't be parsed correctly after they started AviTab, the fallback is also used as described above. Note the latter failure in interactive mode can only happen when the user is explicitly messing up with the config without closing the program. In this case, it means that the user knows what they are doing. In any other case where the config was edited before opening the program, an error message will be shown to the user when starting AviTab (see screenshots in this PR).

This is what the user now will see when they start AviTab with a broken mapconfig.json config:

Once they explicitly acknowledge the error by clicking on the X button of the error window, they can still use AviTab and when they go to the MapApp the default hardcoded fallback (OpenTopoMap) is used:

[fpw]

I understand the issue, but I'm not sure if I like the solution:

• the OpenTopo settings are now duplicated in the code. If any setting ever changes, we need to remember to update two locations - and the code location will be used rather rarely, potentially introducing an unexpected behaviour ("I messed with the map JSON and now I suddenly get red tiles even though OpenTopo worked before?!")
• the logic is rather complicated, I didn't understand the meaning of the new init parameter in the first reading without thinking about your additional comments
• from my understanding, there is no way to reload the JSON config at runtime, i.e. the users have to fully restart X-Plane whenever they're playing with the config. So since fixing errors requires a full and long restart anyways, I don't think it would be much of a drawback to just not provide a failsafe option. They've just edited the map config to test something and it doesn't work, so they'll probably want to fix it immediately.

I'll think about this some more.

[cyberang3l]

from my understanding, there is no way to reload the JSON config at runtime

There is - every time one make changes to the mapconfig.json, closes the menu and goes back to the menu that selects an online map, the mapconfig.json is reloaded. So you don't need to exit X-Plane (or restart AviTab) every time. Just alt-tab to move between X-Plane and the notepad, and reload the menu.