lib: Fix nesting of <p> in install dialog
lib: Fix nesting of <p> in install dialog

`<p>` can only contain inline elements, but `<ul>` is a block element.
Replace the "Additional packages" container with a (nestable) `<div>`.

This does not change the layout.

cockpituous/cockpit,mvollmer/cockpit,deryni/cockpit,garrett/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpituous/cockpit,deryni/cockpit,andreasn/cockpit,moraleslazaro/cockpit,andreasn/cockpit,cockpituous/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,garrett/cockpit,deryni/cockpit,andreasn/cockpit,deryni/cockpit,cockpit-project/cockpit,andreasn/cockpit,garrett/cockpit,martinpitt/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,andreasn/cockpit,garrett/cockpit,mvollmer/cockpit,mvollmer/cockpit,deryni/cockpit,andreasn/cockpit,garrett/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,cockpituous/cockpit,andreasn/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,mvollmer/cockpit,martinpitt/cockpit,deryni/cockpit,deryni/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit