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/Page.php

@@ -0,0 +1,115 @@
+<?php namespace BookStack\Entities;
+
+use BookStack\Uploads\Attachment;
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Collection;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+use Permissions;
+
+/**
+ * Class Page
+ * @property int $chapter_id
+ * @property string $html
+ * @property string $markdown
+ * @property string $text
+ * @property bool $template
+ * @property bool $draft
+ * @property int $revision_count
+ * @property Chapter $chapter
+ * @property Collection $attachments
+ */
+class Page extends BookChild
+{
+    protected $fillable = ['name', 'priority', 'markdown'];
+
+    protected $simpleAttributes = ['name', 'id', 'slug'];
+
+    public $textField = 'text';
+
+    protected $hidden = ['html', 'markdown', 'text', 'restricted', 'pivot'];
+
+    /**
+     * Get the entities that are visible to the current user.
+     */
+    public function scopeVisible(Builder $query)
+    {
+        $query = Permissions::enforceDraftVisiblityOnQuery($query);
+        return parent::scopeVisible($query);
+    }
+
+    /**
+     * Converts this page into a simplified array.
+     * @return mixed
+     */
+    public function toSimpleArray()
+    {
+        $array = array_intersect_key($this->toArray(), array_flip($this->simpleAttributes));
+        $array['url'] = $this->getUrl();
+        return $array;
+    }
+
+    /**
+     * Get the chapter that this page is in, If applicable.
+     * @return BelongsTo
+     */
+    public function chapter()
+    {
+        return $this->belongsTo(Chapter::class);
+    }
+
+    /**
+     * Check if this page has a chapter.
+     * @return bool
+     */
+    public function hasChapter()
+    {
+        return $this->chapter()->count() > 0;
+    }
+
+    /**
+     * Get the associated page revisions, ordered by created date.
+     * @return mixed
+     */
+    public function revisions()
+    {
+        return $this->hasMany(PageRevision::class)->where('type', '=', 'version')->orderBy('created_at', 'desc')->orderBy('id', 'desc');
+    }
+
+    /**
+     * Get the attachments assigned to this page.
+     * @return HasMany
+     */
+    public function attachments()
+    {
+        return $this->hasMany(Attachment::class, 'uploaded_to')->orderBy('order', 'asc');
+    }
+
+    /**
+     * Get the url for this page.
+     * @param string|bool $path
+     * @return string
+     */
+    public function getUrl($path = false)
+    {
+        $bookSlug = $this->getAttribute('bookSlug') ? $this->getAttribute('bookSlug') : $this->book->slug;
+        $midText = $this->draft ? '/draft/' : '/page/';
+        $idComponent = $this->draft ? $this->id : urlencode($this->slug);
+
+        $url = '/books/' . urlencode($bookSlug) . $midText . $idComponent;
+        if ($path !== false) {
+            $url .= '/' . trim($path, '/');
+        }
+
+        return url($url);
+    }
+
+    /**
+     * Get the current revision for the page if existing
+     * @return PageRevision|null
+     */
+    public function getCurrentRevision()
+    {
+        return $this->revisions()->first();
+    }
+}