Advanced application enhancements.

- Turned on CSRF validation by default.
- Added access control for login, signup and logout for frontend application.
- Added access control for login, logout and index for backend application.
- YII_ENV is now defined for all applications.
- No trace is writted to logs if debug is turned off.
- Added default error view for frontend and backend.
- In frontend application captcha will always ask for "testme" if YII_ENV is defined as "test".