Fix bugs

I have fixed some bugs in here:

1. The text will always be in the drop down
![screen shot 2014-12-17 at 7 05 38 pm](https://cloud.githubusercontent.com/assets/6527542/5483014/ce0d06ce-861f-11e4-8859-473843619b45.png)

2. There is a text inside the signup page mentioning @berkeley.edu only
![screen shot 2014-12-17 at 7 04 57 pm](https://cloud.githubusercontent.com/assets/6527542/5483021/e3c31e18-861f-11e4-9c90-1279dbc6bc6a.png)

3. The flash notification for success enroll to class showing up now
![screen shot 2014-12-17 at 7 05 26 pm](https://cloud.githubusercontent.com/assets/6527542/5483023/e9c8eb62-861f-11e4-882d-aee6831769f3.png)

4. When the signup being clicked, there is a text saying mail already sent
![screen shot 2014-12-17 at 7 05 08 pm](https://cloud.githubusercontent.com/assets/6527542/5483024/f092ccf6-861f-11e4-95bf-06c2f99b97f1.png)