[4.0] [Cassiopeia] Move more code to custom modules

[C-Lodder]

Steps to reproduce the issue

The template's index.php should have minimal HTML markup, so we need to start moving some elements to custom modules:

• Header canvas/svg
• Footer (back to top)

[anuragteapot]

@C-Lodder please change build to 4.0 dev

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[ghost]

@Anu1601CS done.

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/19257.}