Add Pokémon gen label to details marker.

[BrownSlaughter]

This adds generation info to RM and adds a small label to the pokemon label window

Motivation and Context

This PR is a precursor to things like "exclude by gen" and "generation % on stats page"

How Has This Been Tested?

Tested and run for a couple of days

needs testing with encounters running to check layout doesnt break

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• [x ] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ x] My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[sebastienvercammen]

RE: Discord: Generation info should be stored in a simple constant, since the generations are just a range of constant IDs. It'll reduce the amount of space needed to store the generation data.

Preferably in map.common.js, e.g.:

// Just as example:
// Gen 1 = [1, 100], Gen 2 = [101, 300], ...
const generations = [
    100,
    300
];

function getPokemonGen(pokemonId) {
    for (var gen = 1; gen <= generations.length; gen++) {
        let genMaxId = generations[gen - 1]
        if (pokemonId <= genMaxId) {
            return gen
        }
    }
    
    // ... this can't happen, Pokémon ID is out of the generation ranges
    console.log('Pokémon ID %s exceeds generation ranges.', pokemonId)
    return -1
}

There are a handful of other reasonable alternatives (simple ifs, and so on) with their pros and cons (this example being easy to add a new generation to).

[sebastienvercammen]

get_pokemon_gen should be done on the front-end, not the back-end.

[sebastienvercammen]

Remove the gen from the back-end data.