Revisit onboarding flow

[bardram]

In the current onboarding flow, the user gets two emails:

1. Update Your Account
2. Study Invitation

We need to revise the wording of these emails and merge them into one email.

Update Your Account

Issues:

• Why is this update needed? Why does the user get this email?
• This needs to be available in Danish too.
• Why the screen with the one button - if only one thing can be done, then why this intermediate step?
• Why do the user need to change their password (this is not my experience that this is needed)?
• If needed, how can the user specify her/his full name?

Study Invitation

Issues:

• This email needs an update - we are no longer "CACHET" but "CARP", etc.
• The font is terrible - too big and cluncky
• Images look terrible (omit those)

[xelahalo]

Add the language selection required action on new account invitation.

[xelahalo]

Take the required actions out if the account that is being invited is not new.

[yuanchen233]

Changed email style at #74 and #71