Make user registration work

[MaHaWo]

• rename AbstractDropdownItem into Select in analogy to Input.
• add elements from Input to Select (Validation, arguments).
• user registration has 2 parts
• primary registration: username + email + password
• these data are saved in a temporary element of the userstore toBeRegistered
• if accepted, get to the next page where you have to put in some personal data for data analysis
• if accepted, user gets added to current userstore and childrenstore
• if not, error messages are given in alert section at the top and elements are highlighted
• newly registered user is set to be logged in right afterwards
• simple attempt at error handling: try-catch --> if error: show alert message in banner
• no further componentization for now.

[lkeegan]

If I register, but then navigate away from the second form before submitting it, I am not a user but I can somehow log in.. maybe it would be simpler to have atomic user creation, where the first form is enough to make a user, then the second form just optionally updates the logged-in users's additional info.

Also the additional logic to make a unique new userid is not going to be used in reality, so maybe simpler to not do it?

Finally it would be better not to expose the password in plain text anywhere, even though the website is fake, people might enter a real username & password.

Otherwise looks good!

[MaHaWo]

• remove logic for user duplication
• fix bug by making registration effective immediatelly
• make password into hashvalue

temp variables for storing user credentials are still there, however. Will be gotten rid of in one of the following PRs that componentizes the input forms again, or at the latest when the backend will be written.

[MaHaWo]

@lkeegan you want to have a look again?

[lkeegan]

lgtm