Updated guides for 7.8

Updated guides fro the 7.8 release

Fixes #2009

See merge request !1531

Fix duplicate authorized applications

On the profile applications page, display one row per authorized app instead of one row per access token.  See #1987.

cc @sytse

See merge request !1524

Remove top margin for issue/mr title

See merge request !1529

Fix double note submit

Closes #1989.

See merge request !1527

Rephrasing in documentation for manual installs

Rephrased the wording in the documentation to say "installation from source" or similar.

/cc @sytse

See merge request !1526

Rephrased wording in the documentation to say "installation from source" instead of  "manual installation" or similar.

Fix typo in changelog

Fixed small typo in changelog file.

Only send "Account was created for you" email when created by admin.

See #1985

cc @sytse

See merge request !1517

Add links to the quick help list

Add links in the quick help list to the pricing and feature comparison pages on about.gitlab.com.  See #1969

cc @sytse

See merge request !1525

Conflicts:
	db/schema.rb

Display the number of unique users with an access token instead of the
total number of access tokens per application in the admin area.

Fix wrong word in document of google oauth

Modify the quick help list to add links to the pricing and feature
comparison pages of about.gitlab.com.

Iterate over authorized applications instead of tokens to avoid multiple
rows for the same authorized app.