add first and last name to svs.sqlite

[sssoleileraaa]

Description

We need a place to store first and last name in the client before we can display them in #411

Add first_name and last_name fields to the users table.

[sssoleileraaa]

also create a hybrid attribute on the users model for journalist initials

Update: a python property will be fine here since we don't need to filter on initials. also create a full name property.

[sssoleileraaa]

When adding the initials attribute to the user model, follow these rules discussed in freedomofpress/securedrop#4251:

• First name and last name, use first character of each word: Nina Vizz -> nv
• First name only, use first two characters: Nina -> ni
• Last name only, use first two characters: Vizz -> vi
• No names in the name fields, use first two characters of username: ninavizz -> ni

[sssoleileraaa]

No names in the name fields, use first two characters of username: ninavizz -> ni

Need to confirm this last rule with @ninavizz, @eloquence, and @ninavizz tomorrow.