HipChat service: correct service name & use v2 API

HipChat refers to their own product camel cased so we should do the
same. HipChat no longer recommends people use the deprecated v1 API so
switch to using the v2 API by default. hipchat-rb does not yet default
to v2 in any version so it must be specified.
HipChat service: support custom servers

HipChat allows users to run their own private servers and to be able to
support those we must connect to the correct URL when using one of these
custom servers.
The blog post will trigger a mail to the list
add preliminary 7.6 upgrade guide

Add preliminary 7.6 upgrade guide. Makes it easier to add upgrades as changes are made rather than trying to round up everything at RC1.

Initial additions:
* Nginx changes needed again in 7.6 as they did not make the final 7.5 upgrade guide
* Suggest that user sets time zone (added in https://github.com/gitlabhq/gitlabhq/pull/8015 but missed in final 7.5 upgrade guide)

Replaces https://github.com/gitlabhq/gitlabhq/pull/8124
Merge branch 'master' of github.com:gitlabhq/gitlabhq
Merge branch 'security-release' into 'master'

Improve security release documentation

I think the MailChimp step is not needed anymore because we automated it.

See merge request !1271
Remove unused password argument from notification

We were still passing a 'password' argument around, but it is not used
anywhere because we send a password reset link in the welcome email
nowadays.
Fix deploy keys permission check in internal api

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Fix internal API for missing project or key

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'remove_password_argument' into 'master'

Remove unused password argument

We no longer put a (random) password in the 'new user' email, so no need to pass it around in the code.

See merge request !1279
Merge branch 'fix-internal-api' into 'master'

Fix internal api

Fixes #1787

See merge request !1280
Show username in comment header for easier mention

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'master' of dev.gitlab.org:gitlab/gitlabhq
Merge pull request #8376 from bbodenmiller/7-6-upgrade-guide

add preliminary 7.6 upgrade guide
Merge branch 'master' of github.com:gitlabhq/gitlabhq
Merge pull request #8283 from cardoe/hipchat-private-server

HipChat custom server support
Merge branch 'username-in-comments' into 'master'

Username in comments

Its hard to mention person in comment if you don't know his username.
This patch show person username right after his name in comment row

See merge request !1281
Change twitter handle from gitlabhq -> gitlab
Merge pull request #8420 from Razer6/change_twitter_handle

Change twitter handle from gitlabhq -> gitlab