Commit [1] solved an unseen issue with the configurator introduced with commit [2].

It was preventing the website configurator to go through in some cases, which was detected on odoo.com/trial the day the 17.1 became available there.

The fix was quickly deployed, but it was actually not enough.. Indeed, Odoo.com trial databases are not created from scratch but indeed are using custom odoo DB images. Those images are not sync'd with the code where they run obviously (we don't create new images everytime we update our /trial production).

Because of that, the fix made at [1] was not enough, as it relied on website module installation. It was quickly done to "revive" the configurator on the production.

The biggest problem is actually the fact that there is no workaround this blocked configurator screen: no skip button, no redirect button, nothing.
That part will be handled in an upcoming task, see [3], which will mitigate the issue as if the configurator were to be blocked again later, there would be a way for the user to "continue".

The fix here is about reverting commit [2] to not take any risk. It means that it will load configurator templates from all themes, even uninstalled ones, but it will reduce the risk of a configurator failure drastically.

Steps to reproduce:
- Checkout git before commit [1]
- Start with `odoo-bin -i website` and design-themes in the addons path.
- Create a new website.
- Generate a website with "About Us", "Services", "Pricing" and "Privacy
Policy".
- ERROR: It will crash
- Now checkout after commit [1]
- Try again the configurator: it will crash. (But note that it will be
  enough to fix DB created after commit [1])
- Now checkout this commit
- Try again the configurator: it works

[1]: https://github.com/odoo/odoo/commit/9ae5e2bb25ea164264aeab7e45f53472a7d6aa5a
[2]: https://github.com/odoo/odoo/commit/cfed4e391d11058b1b46417f0b630cdbc4070d7c
[3]: https://www.odoo.com/web#menu_id=4720&cids=1&action=333&active_id=974&model=project.task&view_type=form&id=3709708