[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/marketing/surveys/overview/create.rst

@@ -14,7 +14,7 @@ When creating your survey, choose a *Title* and *Category*. The *Category* field
 which context the survey is being conducted, as different applications might use it for different
 purposes such as recruitment, certification, or employee appraisal.
 
-.. image:: media/new_survey.png
+.. image:: create/new_survey.png
    :align: center
    :alt: Form view of a survey with a title and category being chosen in Odoo Surveys
 
@@ -36,7 +36,7 @@ Tab: Questions
   displayed as an answer choice, with which a text type field is displayed.
 - *Matrix Type*: choose if you would like to have one or multiple choices per row.
 
-.. image:: media/sections_questions.png
+.. image:: create/sections_questions.png
    :align: center
    :alt: Sections and questions view of a survey in Odoo Surveys
 
@@ -45,7 +45,7 @@ Tab: Description
 
 Write a *Description* to be displayed under the title of the survey's homepage.
 
-.. image:: media/frontend_description.png
+.. image:: create/frontend_description.png
    :align: center
    :alt: Frontend of a survey showing the title and description of a survey for Odoo Surveys
 
@@ -59,7 +59,7 @@ Under the tab *Options*, choose the *Layout* of your questions. If choosing *One
 *One page per question*, an option *Back Button* becomes available, which allows the user to go back
 pages.
 
-.. image:: media/tab_options_layout.png
+.. image:: create/tab_options_layout.png
    :align: center
    :alt: Form view of a survey emphasizing the layout feature under options in Odoo Surveys
 
@@ -71,7 +71,7 @@ Test and share the survey
 | By default, a filter *Except Test Entries* is applied to keep the list of entries clean with only
   real participants.
 
-.. image:: media/user_feedback.png
+.. image:: create/user_feedback.png
    :align: center
    :alt: View list of the participations of a survey in Odoo Surveys
 
@@ -79,7 +79,7 @@ Test and share the survey
   Participations`.
 | Click on *See results* to be redirected to an analytical page.
 
-.. image:: media/analytical_page.png
+.. image:: create/analytical_page.png
    :align: center
    :alt: View of an analytical page for Odoo Surveys