[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#2066

content/applications/finance/payment_acquirers.rst

@@ -188,7 +188,7 @@ The **Capture Amount Manually** field is under the **Configuration** tab. If ena
 reserved for a few days on the customer's card, but not charged yet. Please refer to your acquirer's
 documentation for the exact reservation duration.
 
-.. image:: payment_acquirers/media/capture_manually.png
+.. image:: payment_acquirers/capture_manually.png
    :align: center
    :alt: Configuration tab on Odoo
 
@@ -196,7 +196,7 @@ To capture the payment, you must then go to the related sales order or invoice a
 *capture* the funds before its automatic cancellation, or *void the transaction* to unlock the funds
 from the customer's card.
 
-.. image:: payment_acquirers/media/capture.png
+.. image:: payment_acquirers/capture.png
    :align: center
    :alt: Hold the credit card payment until you capture or revoke it on Odoo
 
@@ -237,7 +237,7 @@ You can use a single journal for many payment methods. And for each payment meth
 - Define an **Accounting Account** to separate these payments from another payment method.
 - Leave blank to fallback on the default account, which you can see or change in the settings.
 
-.. image:: payment_acquirers/media/bank_journal.png
+.. image:: payment_acquirers/bank_journal.png
    :align: center
    :alt: A bank journal in the "Incoming Payments Tab".