Sign up validation

[FelixSeHS]

The following checks are performed before a new profile is created:

1. The username must contain between 3 and 15 characters
2. The entered email adress is an email adress (char '@' is included)
3. The password must contain the following properties: Min. length 6 characters, max. length 35 characters, at least 1 uppercase letter, at least 1 lowercase letter
4. for the password validation the 2nd entered password must be identical with the first one

Only if all the above properties are fullfilled, a new user will be created.

[ElliHuynhHS]

Sign Up validation was implemented and works fine.