Fix the "Add Contacts" button too small in empty label view

Change the "Add Contacts" button style so that clickable area is
larger and meets a11y requirement.
Remove the padding between the text and button.

Screenshots on N5 with clickable area shown:
https://drive.google.com/open?id=0BxaQ3Ze9jz_cWkwwT1p5a2ZrRWc
https://drive.google.com/open?id=0BxaQ3Ze9jz_cb2FFMVhnUXdKT00

Bug 30442846

Change-Id: I34a6bdea0ba52ed5f358633d40d15d94b6e4785f