In 8278b763d9 the default behaviour of annotation
has changes, which was causing a lot of noise in diffs. We decided in #17382
that it is better to get rid of the whole annotate gem, and instead let people
look at schema.rb for the columns in a table.
Fixes: #17382
1. Make the "subscribed" text in Issuable sidebar reflect the labels
subscription status
2. Current user mut be logged-in to toggle issue/MR/label subscription
