Fix EZP-23387: Move image variation config for ezdemo to DemoBundle

> https://jira.ez.no/browse/EZP-23387
> https://jira.ez.no/browse/EZP-23382

Tests have been updated.
Image variations are now dumped for non-ezdemo packages only.

See also [EZP-23382](https://jira.ez.no/browse/EZP-23382). Default image aliases are reduced to the minimum.