simplified way to get tags from associated table

[sfinktah]

A much simpler implementation of #467 which allows tags to be accessed through another table.

No longer requires a separate trait.

Usage:

class Article extends Model
{
    use HasTags;

    public static $taggedModel = OtherModel::class;

[spatie-bot]

Dear contributor,

because this pull request seems to be inactive for quite some time now, I've automatically closed it. If you feel this pull request deserves some attention from my human colleagues feel free to reopen it.

[sfinktah]

@spatie-bot frack you very much