Add password confirmation

Add password confirmation to player module.
Make email and password non-null

Make email and password a non-null field in players table.
Install bcrypt

Install bcrypt-ruby for password hashing.
Implement password hashing

Implement password hashing for user accounts. Rename the password
column in players table to hashed_password.
The hashing is done through bcrypt gem using a static salt and the
default cost for now. These will be change in a future revision when I
have a better idea of what I'm doing.