Added a condition to check password strength

Hi, 
Following the comments on my previous pull request. I have made below changes:
1. A wallet can now be created without any password(this was restricted in my last pull request)
2. A help button is added which explains the restrictions on the password
3. The password should be at least 6 characters, contain an uppercase alphabet and a special character(We can always change these business rules).
4. If the password doesn't have an Upper case alphabet an error message will appear saying so, similarly for special character. I believe this is more user friendly when compared to password strength meter.

Please let me know your thoughts and any additional changes you'd like to have.

Regards,
Azhar