[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/sales/subscriptions/sales_flow/renewals.rst

@@ -30,7 +30,7 @@ have the possibility to renew the subscription. In the Other Info tab, underneat
 section, you can activate the *To renew* option. When activated, a yellow tag automatically appears
 in the upper right corner of the subscription.
 
-.. image:: media/renew-your-subscription.png
+.. image:: renewals/renew-your-subscription.png
   :align: center
   :alt: Renew your subscription with Odoo Subscriptions
 
@@ -39,7 +39,7 @@ in the upper right corner of the subscription.
    on the customer portal. To visualize that, you just have to click on the *Customer preview*
    button. The tag *To renew* appears on the top right corner.
 
-   .. image:: media/customer-preview-of-a-renewal.png
+   .. image:: renewals/customer-preview-of-a-renewal.png
      :align: center
      :alt: Customer preview of a renewal with Odoo Subscriptions
 
@@ -54,7 +54,7 @@ first *Send by email* the quotation to your customers in order to have their con
    from the previous subscription". Once confirmed by your customers, this quotation becomes a
    sales order and a new sale is mentioned in the upper right corner of the subscription.
 
-   .. image:: media/renew-a-quotation.png
+   .. image:: renewals/renew-a-quotation.png
      :align: center
      :alt: Renew a quotation with Odoo Subscriptions
 
@@ -62,7 +62,7 @@ first *Send by email* the quotation to your customers in order to have their con
    The only difference between your two quotations is the description underneath the
    *Subscription Management* category. There, you can easily visualize which one is your renewal.
 
-   .. image:: media/subscription-management-category.png
+   .. image:: renewals/subscription-management-category.png
      :align: center
      :alt: Renewal as Subscription Management form in Odoo Subscriptions
 
@@ -72,7 +72,7 @@ Visualize your subscriptions to renew
 Finally, if you want to visualize all your subscriptions and easily find those to renew, you can go
 to your *Subscriptions dashboard* and use the filter *To renew*.
 
-.. image:: media/subscriptions-dashboard-with-the-to-renew-filter.png
+.. image:: renewals/subscriptions-dashboard-with-the-to-renew-filter.png
   :align: center
   :alt: List view of all subscriptions and use of the filter to renew in Odoo Subscriptions