Improvements to content view

[mmstick]

• Make the list view scrollable
• Place list items into a list column
• Improve styling of list item buttons
• Minor refactoring

[mmstick]

There are some oddities I found that will require adjustments inside libcosmic.

[edfloreshz]

Thanks! 🎉

What specifically needs adjustment?

[mmstick]

I definitely need to finish the list view widget and its button styles. The list column is adding some extra padding on the top and bottom that shouldn't be there, or at lest be configurable. The icon button is no longer as round as it used to be. There's also some layer container component theme issues.

[mmstick]

Should empty lists also show the header?

[edfloreshz]

To maintain consistency between lists I think they should.

[edfloreshz]

Implemented in #3