Closes #5728

[ci skip]

While Safari supports the policy, it does not (currently, as of 9.x)
recognize `origin-when-cross-origin` as a valid value, so we omit the
policy entirely under Safari.

Closes #5609

Closes #4039

This removes the need for Sidekiq and any overhead/problems introduced
by TCP. There are a few things to take into account:

1. When writing data to InfluxDB you may still get an error if the
   server becomes unavailable during the write. Because of this we're
   catching all exceptions and just ignore them (for now).
2. Writing via UDP apparently requires the timestamp to be in
   nanoseconds. Without this data either isn't written properly.
3. Due to the restrictions on UDP buffer sizes we're writing metrics one
   by one, instead of writing all of them at once.

Closes #4295

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

A limited number of pages have defined their own descriptions, but
otherwise we default to the Project's description (if `@project` is
set), or the old `brand_title` fallback.

The image will either be the uploaded project icon (never a generated
one), the user's uploaded icon or Gravatar, or, finally, the GitLab
logo.