Added ability to use templates

- Added replace, append and prepend actions for template content into
both the WYSIWYG editor and markdown editor.
- Added further testing to cover.

app/Http/Controllers/PageTemplateController.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace BookStack\Http\Controllers;
+
+use BookStack\Entities\Repos\PageRepo;
+use BookStack\Exceptions\NotFoundException;
+use Illuminate\Http\Request;
+
+class PageTemplateController extends Controller
+{
+    protected $pageRepo;
+
+    /**
+     * PageTemplateController constructor.
+     * @param $pageRepo
+     */
+    public function __construct(PageRepo $pageRepo)
+    {
+        $this->pageRepo = $pageRepo;
+        parent::__construct();
+    }
+
+    /**
+     * Fetch a list of templates from the system.
+     * @param Request $request
+     * @return \Illuminate\Contracts\View\Factory|\Illuminate\View\View
+     */
+    public function list(Request $request)
+    {
+        $page = $request->get('page', 1);
+        $search = $request->get('search', '');
+        $templates = $this->pageRepo->getPageTemplates(10, $page, $search);
+
+        if ($search) {
+            $templates->appends(['search' => $search]);
+        }
+
+        return view('pages.template-manager-list', [
+            'templates' => $templates
+        ]);
+    }
+
+    /**
+     * Get the content of a template.
+     * @param $templateId
+     * @return \Illuminate\Contracts\Routing\ResponseFactory|\Symfony\Component\HttpFoundation\Response
+     * @throws NotFoundException
+     */
+    public function get($templateId)
+    {
+        $page = $this->pageRepo->getById('page', $templateId);
+
+        if (!$page->template) {
+            throw new NotFoundException();
+        }
+
+        return response()->json([
+            'html' => $page->html,
+            'markdown' => $page->markdown,
+        ]);
+    }
+
+}