Remove hardcoded tile IDs for electrocution

[Vankata453]

Removes hardcoded tile IDs, used for water electrocution in thunderstorm.cpp. They are now defined in the newly created additional category for additional attributes and properties in tileset files.

Importing the water electrocution tile IDs works by adding these data sections in the file, preferably at the end:

 ;; Additional attributes
  (additional
    (thunderstorm
      ;; Attributes for thunderstorm changing tiles
      (changing-tiles
        200  1421
        3419 3523
        3420 3524
        3421 3525
        [more pairs below...]
      )
    )
  )

Fixes #2261.

[weluvgoatz]

My suggestion is that we wait for the tileset PR (#2136) to be finished, and then after that, update tiles.strf in this PR to include the thunderstorm tile changes. Otherwise, this looks good.