draft version of user signin and register

[kimmari1]

Updates:

• Created files xml and java files for RegisterUser and SigninUser
• Created class DatabaseHelper to save user data using SQLite
• Added logo png to drawable

To work on:

• Saving user's task list to the database
• Testing if user login/signin works properly

Helpful things to remember:

• Colour used for background: android:background="#F3ECE7"