md-card action bar padding and margins between icon buttons should be 8px

[asans]

This affects v0.9.0-rc1-master-c964609.

md-card's md-card-footer style uses a padding of 16px. However, based on material specs for cards, it should be 8px.

Of course, it may depend on what is meant by footer in this case. I assume footer can be used as the action bar. However, if the two are significantly different in the use and purpose, there should probably be another style (class="md-action-bar") or element (md-action-bar or something similar to md-dialog) set for this.

Additionally, margins between two normal buttons should be 8px. Right now, it is 8px on each side of the button, creating a total of 16px spacing between two buttons.