Add show password to login

Add a checkbox to the login page that shows the password when checked.
Fixes #124 for the login page.

![screen shot 2014-07-20 at 3 54 28 pm](https://cloud.githubusercontent.com/assets/3108007/3638793/13c1a628-1061-11e4-80de-095ea5597a77.png)
![screen shot 2014-07-20 at 3 53 57 pm](https://cloud.githubusercontent.com/assets/3108007/3638794/18f8507e-1061-11e4-9791-c00a5391b919.png)
^^^ This seems to be github spam.