Use an anchor element for Learn More buttons

[smcmurtry]

From John O'Brien:

"On the list of all benefits pages, the green buttons that link out from a particular benefit exhibit.. non-traditional link based behaviours.

1: There is no mouse-over view of the domain in the browser status bar at bottom of page.
2: Right clicking on button does not present the typical (open in..) experience that one expects with an <a href=>

These combined lead to what I would consider is not-recommended experience in that the user
has no way to determine the safety of clicking on the button. "

[brdunfield]

Related: #1390