Examples: Create progressive web app (PWA)

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And add support for it to the standard library.
Using local storage.
Maybe push notifications?
Maybe hardware access?

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Make the example app the game: "EmojiMemory".
Cards are shown face-down in a 2D grid.
There is a default grid size, say 4 x 3.
The face of the cards are pairs of emoji's, randomly placed.
The player can turn over 2 cards by clicking on them.
If their faces (emojis) match, the cards are left turned,
If they don't match the cards are turned face-down again and it's a new turn.
If all cards are turned with matches, the game is completed.
.
The user can change the grid size when starting the game. (Check when not even).
Turns are counted.
The highscore (lowest score) is remembered per grid size.

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Implemented with latest commit.