Added page content parsing to up-rank header text in search

This adds parsing of page content so that headers apply a boost to
scores in the search term index.
Additionally, this merges title and content terms to reduce the amount
of stored terms a little.
Includes testing to cover.

app/Entities/Models/Book.php

@@ -24,7 +24,7 @@ class Book extends Entity implements HasCoverImage
 {
     use HasFactory;
 
-    public $searchFactor = 2;
+    public $searchFactor = 1.5;
 
     protected $fillable = ['name', 'description'];
     protected $hidden = ['restricted', 'pivot', 'image_id', 'deleted_at'];