This caches the output of Repository#exists? in Redis while making sure
it's flushed properly when creating new repositories, deleting them,
etc.

For the ProjectWiki tests to work I had to make ProjectWiki#create_repo!
public as testing private methods in RSpec is a bit of a pain.

Closes #3026

Closes #3311

These fixes were performed automatically by Rubocop's `-a` flag.

Signed-off-by: NJeroen van Baarsen <jeroenvanbaarsen@gmail.com>

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

From #6168.

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

This reverts commit c46eaca9.

- Database name may contain characters which are not shell friendly
- Database password could contain the same
- While we at it there is no harm in escaping generated paths too
- Refactored 2-line system(command)
Signed-off-by: NNigel Kukard <nkukard@lbsd.net>

This commit replaces the old database backed Wiki system with the
excellent Gollum git based Wiki system.

The UI has been updated to allow for utilizing the extra features
that Gollum provides. Specifically:

* Edit page now allows you to choose the content format.
* Edit page allows you to provide a commit message for the change.
* History page now shows Format, Commit Message, and Commit Hash.
* A new Git Access page has been added with the Wiki Repo URL.
* The default page has been changed to Home from Index to match
the Gollum standard.

The old Wiki model has been left in tact to provide for the
development of a migration script that will move all content stored
in the old Wiki system into new Gollum Wikis.