[MOV] general: removes main "settings" section + move content

This commit is part of a larger work to improve the documentation's
structure. The toctree structure used to add levels to create categories
and make the structure visually more understandable.
With the new version of the documentation, plenty of these categories
are now redundant.

This commit:
- removes the main "settings" section
  - move its content to general/odoo_basics
- moves "general/mobile" content to "general"
- moves the content of the doc "developer_mode/activate" to "general"
  - it replaces the references to that doc with `:ref:` directives
    rather than `:doc:` directives
  - it is worth noting that it also fixes plenty of links that
    previously referred to "developer_mode" (the category) rather than
	"developer_mode/activate" (the document)

task-2535899

content/applications/finance/accounting/fiscal_localizations/localizations/argentina.rst

@@ -274,8 +274,8 @@ with the same letter will share the same sequence.  For example:
 Sequences
 ~~~~~~~~~
 In case that you want to synchronize the next number in the sequence in Odoo based on the next
-number in the AFIP POS, the next button that is visible under :doc:`developer mode
-</applications/general/developer_mode>` can be used:
+number in the AFIP POS, the next button that is visible under :ref:`developer mode <developer-mode>`
+can be used:
 
 .. image:: media/argentina_edi_05.png
    :align: center