Feature: auto-detect map height limit based on generated map

This opens up the true power of the TGP terrain generator, as it
is no longer constrainted by an arbitrary low map height limit,
especially for extreme terrain types.

In other words: on a 1kx1k map with "Alpinist" terrain type, the
map is now really hilly with default settings.

People can still manually limit the map height if they so wish,
and after the terrain generation the limit is stored in the
savegame as if the user set it.

Cheats still allow you to change this value.

src/lang/english.txt

@@ -1206,7 +1206,9 @@ STR_CONFIG_SETTING_CITY_APPROVAL                                :Town council's
 STR_CONFIG_SETTING_CITY_APPROVAL_HELPTEXT                       :Choose how much noise and environmental damage by companies affect their town rating and further construction actions in their area
 
 STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT                             :Map height limit: {STRING2}
-STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_HELPTEXT                    :Set the maximum allowed height of the map; neither the terrain generator nor you can build higher than this limit
+STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_HELPTEXT                    :Set the maximum allowed height of the map; neither the terrain generator nor you can build higher than this limit. On (auto) it will pick a good value after terrain generation
+STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_VALUE                       :{NUM}
+STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_AUTO                        :(auto)
 STR_CONFIG_SETTING_TOO_HIGH_MOUNTAIN                            :{WHITE}You can't set the map height limit to this value. At least one mountain on the map is higher
 STR_CONFIG_SETTING_AUTOSLOPE                                    :Allow landscaping under buildings, tracks, etc.: {STRING2}
 STR_CONFIG_SETTING_AUTOSLOPE_HELPTEXT                           :Allow landscaping under buildings and tracks without removing them