Refresh project authorizations using a Redis lease

This MR changes `User#refresh_authorized_projects` so it uses a Redis lease instead of relying on serializable transactions. See the commit message(s) for more details.

See merge request !7733

Remove caching of events data

This MR removes the caching of events data as this was deemed unnecessary while increasing load on the database. See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6578#note_18864037 and 5371da341e9d7768ebab8e159b3e2cc8fad1d827 for more information.

See merge request !6578

When I proposed using serializable transactions I was hoping we would be
able to refresh data of individual users concurrently. Unfortunately
upon closer inspection it was revealed this was not the case. This could
result in a lot of queries failing due to serialization errors,
overloading the database in the process (given enough workers trying to
update the target table).

To work around this we're now using a Redis lease that is cancelled upon
completion. This ensures we can update the data of different users
concurrently without overloading the database.

The code will try to obtain the lease until it succeeds, waiting at
least 1 second between retries. This is necessary as we may otherwise
end up _not_ updating the data which is not an option.

Add nested groups support to the routing

## What does this MR do?

It allows routing with `/` in namespace name 

## Why was this MR needed?

For nested groups feature(https://gitlab.com/gitlab-org/gitlab-ce/issues/2772). We need URI like `/group/subgroup/project` be routed correctly


## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/2772

See merge request !7459

Flushing the events cache worked by updating a recent number of rows in
the "events" table. This has the result that on PostgreSQL a lot of dead
tuples are produced on a regular basis. This in turn means that
PostgreSQL will spend considerable amounts of time vacuuming this table.
This in turn can lead to an increase of database load.

For GitLab.com we measured the impact of not using events caching and
found no measurable increase in response timings. Meanwhile not flushing
the events cache lead to the "events" table having no more dead tuples
as now rows are only inserted into this table.

As a result of this we are hereby removing events caching as it does not
appear to help and only increases database load.

For more information see the following comment:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6578#note_18864037

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

So that it matches the same access given in
Projects::CreateService#after_create_actions

Remove unnecessary self from user model

self keyword nod needed. Code is more clean and understandable. https://github.com/bbatsov/ruby-style-guide#no-self-unless-required

See merge request !7551