Improve lake generation

Prior to this change, lakes could be very small and could also not be deactivated.

This change allows the deactivation of lake creation and the lake size is now the set size +- 25% instead of anything between 0 and lake_size.

src/lang/english.txt

@@ -1502,6 +1502,8 @@ STR_CONFIG_SETTING_RIVER_TROPICS_WIDTH                          :Tropics width a
 STR_CONFIG_SETTING_RIVER_TROPICS_WIDTH_HELPTEXT                 :Controls the width of the tropic zone that surrounds rivers in sub-tropic landscape.
 STR_CONFIG_SETTING_LAKE_SIZE                                    :Size of lakes: {STRING}
 STR_CONFIG_SETTING_LAKE_SIZE_HELPTEXT                           :Controls the size of lakes that are generated along rivers.
+STR_CONFIG_SETTING_LAKE_SIZE_VALUE                              :{NUM}
+STR_CONFIG_SETTING_LAKE_SIZE_ZERO                               :No lakes
 STR_CONFIG_SETTING_LAKES_ALLOWED_IN_DESERTS                     :Lakes can be generated in sub-tropic climate deserts: {STRING}
 STR_CONFIG_SETTING_LAKES_ALLOWED_IN_DESERTS_HELPTEXT            :Choose whether the lakes that spawn along rivers are allowed in deserts.
 STR_CONFIG_SETTING_RIVER_AMOUNT                                 :River amount: {STRING2}