Moved models to folder, renamed managers to tools

Tools seems to fit better since the classes were a bit of a mixed bunch
and did not always manage.
Also simplified the structure of the SlugGenerator class.
Also focused EntityContext on shelves and simplified to use session
helper.

app/Entities/Models/Deletion.php

@@ -0,0 +1,47 @@
+<?php namespace BookStack\Entities;
+
+use BookStack\Auth\User;
+use BookStack\Interfaces\Loggable;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+
+class Deletion extends Model implements Loggable
+{
+
+    /**
+     * Get the related deletable record.
+     */
+    public function deletable(): MorphTo
+    {
+        return $this->morphTo('deletable')->withTrashed();
+    }
+
+    /**
+     * The the user that performed the deletion.
+     */
+    public function deleter(): BelongsTo
+    {
+        return $this->belongsTo(User::class, 'deleted_by');
+    }
+
+    /**
+     * Create a new deletion record for the provided entity.
+     */
+    public static function createForEntity(Entity $entity): Deletion
+    {
+        $record = (new self())->forceFill([
+            'deleted_by' => user()->id,
+            'deletable_type' => $entity->getMorphClass(),
+            'deletable_id' => $entity->id,
+        ]);
+        $record->save();
+        return $record;
+    }
+
+    public function logDescriptor(): string
+    {
+        $deletable = $this->deletable()->first();
+        return "Deletion ({$this->id}) for {$deletable->getType()} ({$deletable->id}) {$deletable->name}";
+    }
+}