Create user state and insutrctions

[gigicu01]

We need to create a user state and then create instruction to initialize accounts and change the account data when needed (username, dob, country etc.)

[gigicu01]

Update

This issue was partially addressed in PR #35.

To Do List

• Create logic to verify that the input for the change_country function is a country.
• Create logic to verify that the dob input fort he change_dob function is a valid dob.
• Figure out how to make the dob variable a DateTime Variable so we can manipulate it easier.
• Decide exactly what values need to be initialized when creating a user.
• Find out if there is any more data a user account should store.
• Add functions that call on the instructions handlers in lib.rs
• Create tests to verify that a user can be created and he (and only he) can change his own data.