Add optional backend

[angelsk]

• Prompt user with "does this contain an entry form"
• Add basic schema Entry class (ensure two word fields are underscored - ie. first_name)
• Add generated admin module for Entry with csv download
• Include in instructions with information about sfDoctrineGuardPlugin
• Copy Doctrine Guard files access and secure backend in install (include custom Doctrine Guard backend module, basic guard users in fixtures)