[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/accounting/bank/setup/foreign_currency.rst

@@ -43,7 +43,7 @@ After having activated the currencies, you can configure the parameters
 to automate the currency rate update. These options are also in the
 settings of the Accounting application, in the bottom of the page:
 
-.. image:: media/foreign01.png
+.. image:: foreign_currency/foreign01.png
    :align: center
 
 Click on the **Update Now** link to update the currency rates now.
@@ -54,7 +54,7 @@ Create a new bank account
 In the accounting application, we first go to :menuselection:`Configuration -->
 Accounting / Bank account`, and we create a new one.
 
-.. image:: media/foreign02.png
+.. image:: foreign_currency/foreign02.png
    :align: center
 
 Once you save this bank account, Odoo will create all the documents for
@@ -75,13 +75,13 @@ from a supplier in China.
 
 In the :menuselection:`Purchase --> Vendor Bills` , this is what you could see:
 
-.. image:: media/foreign03.png
+.. image:: foreign_currency/foreign03.png
    :align: center
 
 Once you are ready to pay this bill, click on register payment on the
 bill to record a payment.
 
-.. image:: media/foreign04.png
+.. image:: foreign_currency/foreign04.png
    :align: center
 
 That's all you have to do. Odoo will automatically post the foreign
@@ -103,7 +103,7 @@ If you have several invoices with different currencies for the same
 customer, Odoo will split the customer statement by currency, as shown
 in the report below.
 
-.. image:: media/foreign05.png
+.. image:: foreign_currency/foreign05.png
    :align: center
 
 In the above report, the account receivable associated to Camptocamp is