Implemented alternate approach to current joint_permissions

Is a tweak upon the existing approach, mainly to store and query role
permission access in a way that allows muli-level states that may
override eachother. These states are represented in the new PermissionStatus
class.

This also simplifies how own permissions are stored and queried, to be
part of a single column.

app/References/Reference.php

@@ -2,7 +2,9 @@
 
 namespace BookStack\References;
 
+use BookStack\Auth\Permissions\JointPermission;
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Database\Eloquent\Relations\MorphTo;
 
 /**
@@ -24,4 +26,10 @@ class Reference extends Model
     {
         return $this->morphTo('to');
     }
+
+    public function jointPermissions(): HasMany
+    {
+        return $this->hasMany(JointPermission::class, 'entity_id', 'from_id')
+            ->whereColumn('references.from_type', '=', 'joint_permissions.entity_type');
+    }
 }