[FIX] web_editor, website: fix customize_template_get

Commit e11f23b7 split the website
customize_template_get into web_editor and website ones. This split
was not perfect and commit 20861b48
tried to make it work... but did not made it totally and added an
indirect dependency to website module in web_editor...

As the final result is wrong and inconsistent and that the previous
9.0 implementation was already ugly, this was not possible to make
a consistent full-stable fix.

This commit tries to make a fix as stable as possible (the main method
name did not change, the arguments did not change, their purpose is
the same, ...) which makes the code work and be less ugly. However,
the function returns are now slightly different (and JS depends on it).
It returns only valid view information (not header stuff which is not
related to anything and the inherit_id value is now a combination of
the inherit view id and name). Also, a new private method has been
created.

Also, the method contained code which was deprecated since saas-6 but
was never removed (and never broke anything "by chance").

In master these methods will be refactored to make more sense.