lib: set the same padding for all sides of the card headers
lib: set the same padding for all sides of the card headers

Otherwise it looks weird on cards with only the header element.

garrett/cockpit,mvollmer/cockpit,martinpitt/cockpit,deryni/cockpit,deryni/cockpit,mvollmer/cockpit,garrett/cockpit,cockpit-project/cockpit,deryni/cockpit,garrett/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,garrett/cockpit,deryni/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,deryni/cockpit,martinpitt/cockpit,garrett/cockpit,mvollmer/cockpit,deryni/cockpit,deryni/cockpit