Add "generation" pokemon is available in, in pokemon_details.html

[LAMaglan]

Shows up like this:

"sprites"{
   "versions":{
      "generation-i": {<data>},
      "generation-ii": {<data>},
      ...
   }
}

i.e., if generations-<roman numeral> is present, then it exists for that generation, and conversely, if missing, it does not exist in that generation.

[LAMaglan]

Have under header "Other" or similar

[LAMaglan]

Note: cannot simply do generation X to generation Y, because some pokemon can be unavailable in between generations.

[LAMaglan]

Have as a simple list? Available in generation 1, generation 2, generation 3, ... ?