U4-9914 - UserController method to upload an avatar and set password when receiving invite

@madsrasmussen assigning to you (copying notes from our convo):

Basically all of the invite stuff is working all the way through to setting the password and setting the avatar but you'll need to:

• Test it so you can get an invite link generated - ask Claus how you can set up your SMTP settings to use specifiedPickupDirectory so that all emails sent go to files
• Click on the link, you'll get taken to the set password screen, you can then set a password, all validation is wired up too
• Once done, you'll be fully logged in and you won't be able to use that link anymore
• You'll see the avatar screen - it's ugly because i've borrowed parts from other places which you'll see in the markup. It 'should' show any gravatar that is assigned to that email address (but i haven't tested that). Then you can click the plus to select and upload an image, the progress bar will also display if it's slow. When it's done the cancel button is gone and you can click the green button to continue and you will be fully logged in

TODO:

• Fix the avatar design after the invite
• We need to fix setting the avatar so that the avatar in the top right corner of the back office is updated, this goes for both setting the avatar from the invite and also from setting it in the user section for the current user
• Wire up the Skip button if the user doesn't want to set the avatar (sorry i should have done this so i can do it tomorrow if you don't get there)

Putting this one in reopened for @madsrasmussen to pick up.

The issues with the emails have been resolved in another issue, so it should be possible to work on this now.

I fixed up the UI bits here: f87245f73d348c95989ac6a78269502cd88609b3