Fixes #3851

Closes #201 - two-year-old bug, woo!  

These methods no longer include public groups/projects (that don't
belong to the actual user) as this is handled by the various finder
classes now. This also removes the need for passing extra arguments.

Note that memoizing was removed _explicitly_. For whatever reason doing
so messes up the users controller to a point where it claims a certain
user does _not_ have access to certain groups/projects when it does have
access. Existing code shouldn't be affected as these methods are only
called in ways that they'd run queries anyway (e.g. a combination of
"any?" and "each" which would run 2 queries regardless of memoizing).

This new setup no longer loads any IDs into memory using "pluck",
instead using SQL UNIONs to merge the various datasets together. This
results in greatly improved query performance as well as a reduction of
memory usage.

The old setup was in particular problematic when requesting the
authorized projects _including_ public/internal projects as this would
result in roughly 65000 project IDs being loaded into memory. These IDs
would in turn be passed to other queries.

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

The descriptions were not accurate and one particular spec seemingly
expected the wrong User row to be returned.

[ci skip]

This simplifies the "Report button" to not use open a dropdown and
adds a tooltip on this button.
This also removes an extra spec and adds missing specs.

Only show recent push event if the branch still exists or a recent merge request has not been created

Closes #2277

Closes #2116
Closes https://github.com/gitlabhq/gitlabhq/issues/9502

This method encapsulates all the logic for disabling 2FA on a specific
User model.

- Removes looking up authors/committers by name
- Renames `User.find_for_commit` to `User.find_by_any_email`

Now it executes a single query instead of a possible three at the cost
of some scary-looking ARel calls.

Now we can simply loop through all themes, among other things.

This also removes the `dark_theme` / `light_theme` classes and the
`theme_type` helper, since they weren't used anywhere.

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: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Snippet model was missing project association

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