[MOV] content/*: move resource files into their related page's directory

Since odoo/documentation#903, the guideline for the location of new
resource (images, downloadable files, RST includes...) files is to place
those inside the directory of the RST page that references them.

For example, if `doc1.rst` has a reference to `image.png` and to
`download.zip`, the file structure should look like this:

├── parent_doc/
│     └── doc1/
│     │     └── image.png
│     │     └── download.zip
│     └── doc1.rst
│     └── doc2.rst
├── parent_doc.rst

Before this commit, most of the resource files were still located inside
'media' directories holding all the resource files referenced by RST
pages located at the same level as these directories. In the example
above, a single 'media' directory would hold all the resource files
referenced by both `doc1.rst` and `doc2.rst`. Doing so prevented us from
figuring out easily which resource file was referenced by which RST page
and, thus, lead to unused resource files piling up in the repository. It
also made it more complicated to define codeowners regex rules because a
team could not simply be assigned to `/some_page.*` but needed to be
assigned to both `/some_page\.rst` and to the location of 'media'.

In order to help new content writers figure out the guideline when
taking examples from other RST pages, this commit retroactively applies
the guideline to existing resource files and 'media' directories. The
left-over resource files that are not referenced by any RST page are
removed.

task-2497965

Part-of: odoo/documentation#2068

content/applications/websites/ecommerce/maximizing_revenue/reviews.rst

@@ -6,7 +6,7 @@ Publishing and monitoring customer experience will help you gain the trust
 of new customers and better engage with your community. In 2 clicks, allow
 your customer to share their feedback!
 
-.. image:: ./media/comment_post.png
+.. image:: reviews/comment_post.png
    :align: center
 
 Setup
@@ -14,7 +14,7 @@ Setup
 
 Activate comments & rating from the *Customize* menu of the product web page.
 
-.. image:: ./media/comment_setup.png
+.. image:: reviews/comment_setup.png
    :align: center
 
 .. note::
@@ -27,7 +27,7 @@ Review the posts in real time
 Whenever a post is published, the product manager and all the product followers
 get notified in their Inbox (*Discuss* menu).
 
-.. image:: ./media/comment_new.png
+.. image:: reviews/comment_new.png
    :align: center
 
 .. note::
@@ -36,7 +36,7 @@ get notified in their Inbox (*Discuss* menu).
 Click the product name to open the detail form and review the comment (in the
 product discussion thread).
 
-.. image:: ./media/comment_inbox.png
+.. image:: reviews/comment_inbox.png
    :align: center
 
 Moderate & unpublish
@@ -48,12 +48,12 @@ or on the web page.
 To unpublish the post, open the product web page and click the *Published* button
 to turn it red (*Unpublished*). 
 
-.. image:: ./media/comment_unpublish.png
+.. image:: reviews/comment_unpublish.png
    :align: center
 
 ..tip::
     You can access the web page from the detail form by clicking the *Published*
     smart button (and vice versa).
 
-.. image:: ./media/comment_webpage.png
+.. image:: reviews/comment_webpage.png
    :align: center