[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/point_of_sale/payment/ingenico.rst

@@ -29,7 +29,7 @@ Box* (you can find it on the form view of your IoT Box). Then, enter
 9000 as port. The terminal will restart. Once it is done, go on your
 *IoT Box* form in Odoo and verify that the terminal has been found.
 
-.. image:: media/payment_terminal_02.png
+.. image:: ingenico/payment_terminal_02.png
    :align: center
 
 Configure the payment method
@@ -38,7 +38,7 @@ Configure the payment method
 First, go in the general settings of the POS app, and activate the
 Ingenico setting.
 
-.. image:: media/payment_terminal_03.png
+.. image:: ingenico/payment_terminal_03.png
    :align: center
 
 Go back in :menuselection:`Point of Sale --> Configuration --> Point of Sale`,
@@ -46,7 +46,7 @@ go in the payments section and access your payment methods. Create a new
 payment method for Ingenico, select the payment terminal option Ingenico, and
 select your payment terminal device.
 
-.. image:: media/payment_terminal_04.png
+.. image:: ingenico/payment_terminal_04.png
    :align: center
 
 Pay with a payment terminal
@@ -58,7 +58,7 @@ column is the one that has to be sent to the payment terminal and click
 on *Send*. When the payment is successful, the status will change to
 *Payment Successful*.
 
-.. image:: media/payment_terminal_05.png
+.. image:: ingenico/payment_terminal_05.png
    :align: center
 
 If you want to cancel the payment request, click on cancel. You can
@@ -76,5 +76,5 @@ issues.
 Once your payment is processed, on the payment record, you’ll find the
 type of card that has been used and the transaction ID.
 
-.. image:: media/payment_terminal_06.png
+.. image:: ingenico/payment_terminal_06.png
    :align: center