Prevent database query each time we render group avatar

Fixes #2118

See merge request !1688

Fix email images

## Dependencies:
This MR Depends on gitlab-org/html-pipeline-gitlab!4 being **merged and published** to rubygems.org

## What does this MR do?
This MR fixes the broken images in emails that occured scince we introduced access control for all attachments in 7.8.
The access control lead to broken images, because the user usually isn't logged into gitlab when opening the email in his mail client.
The solution to fix this, is to replace all images that were uploaded to gitlab as attachemnts with inline images in emails.

I only added one test for images in notes, because all notes share the same view. If it works fine for a note on a commit, then it'll also work the same for notes on a MR or on issues.

@DouweM can you review this please?

Closes #1161

See merge request !373

Fix missing GitHub organisation repositories on import page.

Private repositories belonging to organizations rather than users can't be imported because `client.repos(org.login)` was requesting `/users/:org_login/repos` (which only returns public org repo's), while we need `/orgs/:org_login/repos` (which includes both public and private). The `client.org_repos` method does this.

cc @marin This is a bug in 7.8.x, but I'm not sure if it needs a minor release now or if it can go in 7.9.

See merge request !1683

This adds the functionality of replacing all images that were uploaded
to gitlab with inline images(base64) in emails.
This change fixes the broken images in emails that 7.8 introduced

 Fix code preview theme setting for comments, issues, merge requests, and snippets

User color scheme was not being used: default white color scheme was always chosen. Also, default background for code in notes was always overriding the user color scheme.

Closes #1139

See merge request !357