[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/finance/accounting/taxation/taxes/taxes.rst

@@ -19,7 +19,7 @@ default, so that you can activate only the ones relevant for your business.
 To activate Sale Taxes, go to :menuselection:`Accounting --> Configuration --> Taxes` and use the
 *Activate* toggle button to activate or deactivate a tax.
 
-.. image:: media/taxes-list.png
+.. image:: taxes/taxes-list.png
    :align: center
    :alt: Activate pre-configured taxes in Odoo Accounting
 
@@ -31,7 +31,7 @@ Configuration
 To edit or create a **Tax**, go to :menuselection:`Accounting --> Configuration --> Taxes` and open
 a tax or click on *Create*.
 
-.. image:: media/taxes-edit.png
+.. image:: taxes/taxes-edit.png
    :align: center
    :alt: Edition of a tax in Odoo Accounting
 
@@ -156,7 +156,7 @@ Definition tab
 Allocate with precision the amount of the taxable basis or percentages of the computed tax to
 multiple accounts and Tax Grids.
 
-.. image:: media/taxes-definition.png
+.. image:: taxes/taxes-definition.png
    :align: center
    :alt: Allocate tax amounts to the right accounts and tax grids
 
@@ -183,7 +183,7 @@ The label of the tax, as displayed on each invoice line in the **Taxes** column.
 :ref:`label <taxes/labels>` visible to *front end* users, on exported invoices, on their Customer
 Portals, etc.
 
-.. image:: media/taxes-invoice-label.png
+.. image:: taxes/taxes-invoice-label.png
    :align: center
    :alt: The Label on Invoices is displayed on each invoice line
 
@@ -198,7 +198,7 @@ Select to which **Tax Group** the tax belongs. The Tax Group name is the :ref:`l
 Tax groups include different iterations of the same tax. This can be useful when you must record
 differently the same tax according to :doc:`Fiscal Positions <fiscal_positions>`.
 
-.. image:: media/taxes-invoice-tax-group.png
+.. image:: taxes/taxes-invoice-tax-group.png
    :align: center
    :alt: The Tax Group name is different from the Label on Invoices
 
@@ -258,7 +258,7 @@ the same product.
 You can configure a new :ref:`Group of Taxes <taxes/computation>` to include this tax, or add it
 directly to a product line.
 
-.. image:: media/taxes-subsequent-line.png
+.. image:: taxes/taxes-subsequent-line.png
    :align: center
    :alt: The eco-tax is taken into the basis of the 21% VAT tax
 
@@ -270,7 +270,7 @@ directly to a product line.
    To reorder the sequence, go to :menuselection:`Accounting --> Configuration --> Taxes`, and drag
    and drop the lines with the handles next to the tax names.
 
-   .. image:: media/taxes-list-sequence.png
+   .. image:: taxes/taxes-list-sequence.png
       :align: center
       :alt: The taxes' sequence in Odoo determines which tax is applied first