Add new emoji-layout

Screenshots

The numbers 1 to 10 choose a broad category of emojis ("food", "animals", "smileys", and other categories). Within each of these categories, there are groups of more closely related emojis (for example: "fruits", "vegetables", "drinks", and more, for the "food"-category). These groups are represented by an emoji from the group with a + next to it. Pressing any of those keys, will open a view with the emojis in that group. There may be additional views in those groups, that can be accessed with the arrows that may appear on the right and left sides of the layout, if not all emojis in the group can be displayed in one view.

There are more than 1000 emojis available in this layout; sorted into categories and groups, according to the recommended ordering from the Unicode Emoji Charts v15.1.

Fixes #381 (closed)

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These emoji-layouts can be used by placing us.yaml and us_wide.yaml in ~/.local/share/squeekboard/keyboards/emoji/, and then switching to the emoji-layout in Squeekboard.