Password Reset UI

FE part of pleroma#114 (closed)

(This spec is WIP, additions / changes are very welcome)

Password Reset

• Add a new form containing email field and submit button (clarify whether we need to use nickname instead of email — BE supports both, see pleroma!531 (merged))
• Add navigation to that form ("Forgot password?" link next to Register link in Login form? We don't seem to have it in current translations, though)
• On submit, do POST to /api/account/password_reset (note: email parameter takes precedence over nickname on BE)
• On 204 No Content, redirect to login form (main screen) -or- display "Password reset link sent!" message (prevent submitting the form more than once for unauthenticated users, though admins might want to submit it numerous times for different users — TBD)
• On error response, display the error

Post-registration changes

• Only if /statusnet/config has accountActivationRequired set to 1, display message that user needs to check mailbox for account confirmation email prior to logging in (clarify the exact wording). Also, registration action will render pleroma.confirmation_pending as true in this case (see pleroma!546 (merged)).

P.S. "Invite via Email" part moved to #192 (comment 10034)