Be specific about the style for suggested-action

Add use the existing style only in .header-bar.
Don't show the focus outline on message dialog buttons

We already style the border.
Don't show a bottom border on the message dialog buttons

They are supposed to be abutting the dialog edge. Although
it is unfortunate that we rely on synchronized mutter themes for this.
Use the selection color for the suggested action on message dialogs
Revert "Be specific about the style for suggested-action"

This reverts commit 9d80d64e36e09b8e3a555a10382fd33eab25701b.
Revert "Use the selection color for the suggested action on message dialogs"

This reverts commit ea030ea6dd29770d1c6ec4c36c0599fa6865404e.
Don't add a box shadow on the suggested button when linked
Make font changes apply to header bar titles

It is enough to set weight and size for the title / subtitle.

https://bugzilla.gnome.org/show_bug.cgi?id=723240