Rename fields in users database schema #32

In efforts to be consistent with a single naming convention, some fields need to be renamed
wool_destroys -> monumentDestroys
wool_pickups -> woolPickups
wool_placements -> woolPlacements

These should ideally be eventually moved into gamemode specific stat sections, along the lines of:

{
    "name": "Notch",
    "kills": 100,
    "deaths": 38579,
    ...
    "gamemodes": {
        "DTM": {
            "monumentDestroys": 15
        },
        "CTW": {
            "woolPickups": 24,
            "woolPlacements": 9,
        },
        ...
    }
}