[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/others/adviser/budget.rst

@@ -24,14 +24,14 @@ First we need to install the relevant apps to use budgeting. The main
 module is the accounting app. Go in the app module and install the
 **Accounting and Finance** app.
 
-.. image:: media/budget01.png
+.. image:: budget/budget01.png
    :align: center
 
 Further configuration is as well necessary. Go to :menuselection:`Accounting
 module --> Configuration --> Settings` and enable the **Budget
 management** feature
 
-.. image:: media/budget02.png
+.. image:: budget/budget02.png
    :align: center
 
 Budgetary Positions
@@ -62,18 +62,18 @@ Budgetary Positions`.
 For our example we need to define what accounts relates to our project's
 expenses. Create a position and add items to select the accounts.
 
-.. image:: media/budget03.png
+.. image:: budget/budget03.png
    :align: center
 
 In this case we select the three relevant accounts used wherein we will
 book our expenses.
 
-.. image:: media/budget04.png
+.. image:: budget/budget04.png
    :align: center
 
 Click on *Select*.
 
-.. image:: media/budget05.png
+.. image:: budget/budget05.png
    :align: center
 
 Save the changes to confirm your Budgetary position.
@@ -91,7 +91,7 @@ analytical account by entering the Accounting module and clicking
 :menuselection:`Advisers --> Analytic Accounts --> Open Charts`. Create a new Account
 called Smith&Co project and select the related partner.
 
-.. image:: media/budget06.png
+.. image:: budget/budget06.png
    :align: center
 
 Set a budget
@@ -108,7 +108,7 @@ We have to give a name to the budget. In this case we'll call it "Smith
 Project". Select the period wherein the budget will be applicable. Next
 add an item to specify your targets in the Budget Line.
 
-.. image:: media/budget07.png
+.. image:: budget/budget07.png
    :align: center
 
 Select the Budgetary Position related to the Budget Line. In other
@@ -118,7 +118,7 @@ Select the "Cost" Budgetary Position and specify the Planned Amount.
 As we are recording a cost, we need to specify a **negative amount**.
 Finally, select the corresponding analytic account.
 
-.. image:: media/budget08.png
+.. image:: budget/budget08.png
    :align: center
 
 Click on **Save & new** to input the revenue budget. The Budgetary
@@ -146,7 +146,7 @@ Via the analytical account, Odoo can account the invoice lines and
 purchase lines booked in the accounts and will display them in the
 **Practical Amount** column.
 
-.. image:: media/budget09.png
+.. image:: budget/budget09.png
    :align: center
 
 .. note::