Fix memory and performance issues in Karma test suite

Closes #45900 and #45806

See merge request gitlab-org/gitlab-ce!18658

Bump nokogiri to 1.8.2 in qa Gemfile

See merge request gitlab-org/gitlab-ce!18673

Use gitaly 0.96.2

See merge request gitlab-org/gitlab-ce!18670

Fix commit trailer rendering when Gravatar is disabled

Closes #45633

See merge request gitlab-org/gitlab-ce!18586

Resolves CVE-2017-18258

Use gitlab-workhorse 4.2.0

See merge request gitlab-org/gitlab-ce!18671

Use persisted diff data instead fetching Git on discussions

Closes #44052

See merge request gitlab-org/gitlab-ce!18657

Add alpine mirrors while operating on k8s cluster

Closes gitlab-ee#4922

See merge request gitlab-org/gitlab-ce!18651

Merge request and commit discussions API

Closes #20901

See merge request gitlab-org/gitlab-ce!18537

Use Ruby methods, not Rails' String#first

See merge request gitlab-org/gitlab-ce!18669

[CE] Exclude LDAP from OmniauthCallbackController base methods

See merge request gitlab-org/gitlab-ce!18619

show only groups an admin is a member of in dashboards/grops

See merge request gitlab-org/gitlab-ce!17884

Gitaly-Ruby is not a Rails application, which made the method not exist
after the vendor. This patch uses direct indexing, which has the same
properties that `#first` has.

Found while working on: https://gitlab.com/gitlab-org/gitaly/merge_requests/699

Update timeline icon for description edit

Closes #39946

See merge request gitlab-org/gitlab-ce!18633

Fix spec/features/projects/issues/user_toggles_subscription_spec.rb

Closes #45918

See merge request gitlab-org/gitlab-ce!18666

Revert discussion counter height

Closes #45896

See merge request gitlab-org/gitlab-ce!18656

Today, when fetching diffs of a note, we always go to Gitaly in order to diff between commits and return the diff of each discussion note. With this change we avoid doing that for notes on the "current version" of the MR.