KConfigXT migration for power state profiles

This commit adds a new PowerDevil::ProfileSettings class, generated
from PowerDevilProfileSettings.kcfg via KConfig compiler / KConfigXT.
Only new configuration entries are introduced here, no behavior
changes yet for code that still relies on older configuration.

These settings represent the same data as before, but categories
and config entry naming has been cleaned up / reimagined because
the existing powermanagementprofilesrc structure cannot be reused
as is. KConfigXT settings classes can't check for the existence of
config groups like the current hand-written KConfig code.

So we're migrating all profile configuration to powerdevilrc
using the new structure, and we keep powermanagementprofilesrc
in place to avoid breaking users who switch back to Plasma 5.

Includes migration tests with before & after config files,
demonstrating the changes compared to Plasma 5 profile configs.

Fixes powerdevil issue #3.