Add "notes" to each candidate in soviet

[lvps]

Add an editable "notes" textbox in soviet-read.xhtml, so we can add stuff like "Ask for details on X during interview" or "Rejected because X, Y and Z". Visible to admins only, obviously.

[steemnd]

Can be solved by adding an additional table and then join on tg_user.user_id

[lvps]

Sure, but that would still require modifications to the production database, so there's not a lot of difference from the "joinless" version