Add role="search" to the database search form

Apparently, for accessibility reasons, the search form of a page should be tagged with role="search"
http://wiki.accede-web.com/en/notices/html-css/identifier-les-principales-zones-de-la-page-avec-l-attribut-role?s[]=role&s[]=search

This is done in the form of the Main.Search page as well as global search form, but we should also do it for the database search form. /xwiki/bin/view/Main/DatabaseSearch

Detect the issue:

1. Go to Database Search page (/xwiki/bin/view/Main/DatabaseSearch). Here you will find the Database search form (below is the screenshot).
2. Using your browser's Developer Tools, inspect the form and you will find that role="search" is missing for Database Form.
3. In order to fix it, you have to go to the search component `xwiki-platform-search` and locate the form and fix it. 

Prerequisites

Familiarize yourself with XWiki by downloading and installing the latest version.

Try to reproduce the issue described by the task. You should use your browser's Developer Tools to identify and test your solution.

Once you have reproduced the issue presented in the task, it's time to identify the location where it needs to be fixed in the code.
You should be familiar with using Git locally or you might be able to commit your changes from the GitHub interface.

The task will give you hints about the component where the code with the problem is located. Identify the file, make the changes and submit a Pull Request for mentors to approve and close the task. Don't forget to add screenshots with before and after your changes.

Requirements

• Knowledge of HTML, XML, basic programming, Git
• You will encounter concepts like Data Model, Skins Extensions, Templating engines, Apache Velocity, modular components, etc. but you don't need to be familiar with them in advance

Expected Outcome

• Pull Request on the https://github.com/xwiki/xwiki-platform repository with the solution
• The summary of the Pull Request must have the first-line matching the JIRA issue following by a colon and then the title of this issue
• Following best practices defined at http://dev.xwiki.org/xwiki/bin/view/Main/WebHome