Add sentry integration
Sentry is an event logging platform primarily focused on capturing and
aggregating exceptions. With this MR it will be possible to log and
track exceptions from GitLab to Sentry.
https://gitlab.com/gitlab-com/operations/issues/39
See merge request !2485
Allow access to artifacts for users with reporter role
This is originally introduced by @ajohnsn in this merge request: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2259
I've added and refactored specs, original commit by @ajohnsn has been cherry picked here.
See merge request !2448
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Closes#3437


See merge request !2068
LDAP Sync blocked user edgecases
Allow GitLab admins to block otherwise valid GitLab LDAP users
(https://gitlab.com/gitlab-org/gitlab-ce/issues/3462)
Based on the discussion on the original issue, we are going to differentiate "normal" block operations to the ldap automatic ones in order to make some decisions when its one or the other.
Expected behavior:
- [x] "ldap_blocked" users respond to both `blocked?` and `ldap_blocked?`
- [x] "ldap_blocked" users can't be unblocked by the Admin UI
- [x] "ldap_blocked" users can't be unblocked by the API
- [x] Block operations that are originated from LDAP synchronization will flag user as "ldap_blocked"
- [x] Only "ldap_blocked" users will be automatically unblocked by LDAP synchronization
- [x] When LDAP identity is removed, we should convert `ldap_blocked` into `blocked`
Mockup for the Admin UI with both "ldap_blocked" and normal "blocked" users:

There will be another MR for the EE version.
See merge request !2242
Show referenced MRs & Issues only when the current viewer can access them
This addresses both issues identified in #6066.
## The private MR by user `remy2` with a note referencing to a public issue

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## The public issue viewed by user `remy` **who doesn't have access to `remy2/private-project`** before the fix

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## The public issue viewed by user `remy` **who doesn't have access to `remy2/private-project`** with the fix

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## The public issue viewed by user `remy2` with the fix (no change)

See merge request !2405
This is intended to prevent the user from creating new objects while the
transaction that removes them is being run, resulting in objects with
nil authors which can then not be edited.
See https://gitlab.com/gitlab-org/gitlab-ce/issues/7117
Improve performance of getting issues on group level
For testing I used the URL http://localhost:3000/groups/gitlab-org/issues?milestone_title=8.1. Prior to these changes said URL would take about 10-12 seconds to load. By applying these changes the loading time has been reduced to roughly 2-3 seconds.
There's still some stuff going on in some views that I have to look at, resolving those changes might reduce the loading time a bit more. I also still have to check if I didn't break too many tests.
Fixes: gitlab-org/gitlab-ce#3707 gitlab-org/gitlab-ce#4071
See merge request !2318