Added comments controller, model, repo, and the database schema. Modified existing Page model to associate with comments.

app/Comment.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace BookStack;
+
+class Comment extends Ownable
+{
+    protected $fillable = ['text', 'html'];
+    
+    /**
+     * Get the entity that this comment belongs to
+     * @return \Illuminate\Database\Eloquent\Relations\MorphTo
+     */
+    public function entity()
+    {
+        return $this->morphTo('entity');
+    }
+    
+    /**
+     * Get the page that this comment is in.
+     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function page()
+    {
+        return $this->belongsTo(Page::class);
+    }
+    
+    /**
+     * Get the owner of this comment.
+     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function user() 
+    {
+        return $this->belongsTo(User::class);
+    }
+}