Support for Media Files

Minor change in this patch so it applies to 3.x (file_url_transform_relative() method deprecation).

In an attempt to test this, I created a new site, then, I went to /admin/structure/types/manage/article/fields/add-field, and added a new field of type Reference > File which allows PDF imports.

Then I went to /node/add/article and created an article named "test" with a PDF import.

Then I went to /admin/content/files and noted the file's ID, which is 1.

Then I went to /admin/config/content/formats/manage/full_html?destination=/admin/config/content/formats and checked "Convert Legacy Media Tags to Markup", and saved.

Then I opened /node/add/page and created a page called "Test page".

In it, I added in the source code:

[[{"link_text":"this is a test","fid":"1"}]]

In text format "Full HTML".

Then I saved, but on the end page, I could see the following:

[[{"link_text":"this is a test","fid":"1"}]]

And not

this is a test →

If you would like me to commit the patch to the next version of the module, please provide a complete step-by-step guide to testing it, thanks!