Add a tabs example to the pattern library
Turn forgot password button back into a button
Improve tab styles on the authentication forms

Previously the active tab would be red, which could be confused with our
red anchor text and make the other tab look disabled. The new design
makes all text gray but adds an "active" border below the button.
Use border only on active nav-tabs item
Merge pull request #1352 from hypothesis/improve-tabs

Improve usability of sheet tabs