Added AES encryption/decryption ability (version 1)
-AesInterface is a Qt interface for AES encryption/decryption
   that uses AES 256 CBC mode.
[PasswordManager] change return type of updateEntry()  to bool.
[PasswordManager] Moved saving selected backend to switchBackend().

-Also added PasswordManager::passwordBackendChanged() signal.
-Also some other options moved to AutoFillManager::currentPasswordBackendChanged()
[PasswordManager] Added DatabaseEncryptedPasswordBackend.

-It uses AesInterface for all encryption/decryption (AES 256 CBC)
[DatabaseEncryptedPasswordBackend] Added tests.
[Windows][Tests] Fixed compile issues on Windows.
[MasterPasswordDialog] Fixed, clear masterpassword always changes backend.
-Also fixed recursive call to QDialog::exec()