Closes https://github.com/gitlabhq/gitlabhq/issues/9328

To prevent loose of group data you need to transfer or remove group
first before you can remove user
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

**What does this do?**
It removes the very strict sanitation on the users bio field, so that people can
have a bio like "I <3 GitLab"

**Why is this needed?**
Currently when you enter a bio with "I <3 GitLab", we only store "I ". This is
unexpected behaviour, since we want users to have a normal profile, without
having to worry what characters are allowed and which are not.

**Related issues:**
Fixes https://github.com/gitlabhq/gitlabhq/issues/5625Signed-off-by: NJeroen van Baarsen <jeroenvanbaarsen@gmail.com>

Now there is a single source of information for which attribute a model
uses to be referenced, and its special character.

This would result in a 404 error in certain views.

The `save` call was being rolled back due to an error in the validation step.
Relax the validation step so that this works.

Closes #1570

This feature was requested long ago:

http://feedback.gitlab.com/forums/176466-general/suggestions/4118466-ability-to-register-only-from-ceratain-domains

This MR is based off !253 but changed to use application settings and use wildcard strings
to give more flexibility in pattern matching. Regexps seemed overkill and easy to get wrong.

Only restrict e-mail addresses upon creation

This reverts commit c0116926.

This commit allows user to show one of their emails in profile page,
or don't show email in this page.