Implement Freeplay tabs

[x8c8r]

This is a pretty rough implementation of Freeplay tabs.

Tabs are defined in the a data/freeplay.json file with the following format:

{
  "tabs": [
    {
      "title": "Tab Title",
      "songs": ["song-one", "song-two", "song-three"]
    }
  ]
}

If there are no tabs defined - The engine resorts back to old Freeplay behaviour and creates it using weeks instead.

Tabs can be scrolled through by pressing TAB. Holding shift makes you scroll backwards.

You may notice that none of the songs have icons:

That's because icon, bg color and display name for songs should be defined in the song's meta.json file like this:

{
    "songName": "dadbattle",
    "displayName": "Dad Battle",

    "freeplayColor": "#9457EB",
    "freeplayIcon": "dad"
}

If this gets merged I'll personally go through every single base game song and add metadata to them.
Edit: And i did.

Let me know if anything should be changed.

[x8c8r]

please speed

[BeastTornado]

Please speed I neeeed this. My Freeplay's kinda tabless....