Handle duplicate appearances table creation issue with upgrade from CE to EE

Closes #391

See merge request !278

Hide builds from Project's settings when the feature is disabled (EE)

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/13944

See merge request !268

Geo: ReadOnly middleware improvements

We should handle API requests (JSON) in a different way we handle normal requests.

Current implementation always redirect to root and display error messages using `flash[:alert]`.
This MR adds `{ message: "..." }` type of response when request is under `application/json` content_type.

This is a small patch/enhancement for Geo (#76)

See merge request !274

Closes #391

Ensure GithubImport::Client does not crash when the 'verify_ssl' config is not present

This fixes gitlab-org/gitlab-ce#14343 and !260 when `verify_ssl` is not present in the GitHub omniauth
settings in `gitlab.yml`.

Settingslogic allow to access optional settings through the Hash
notation: if the key is not present, it returns nil. In the present case
this will let the Octokit::Client object use whatever default value it
wants for the ssl option.

/cc @dbalexandre 

See merge request !275

Settingslogic allow to access optional settings through the Hash
notation: if the key is not present, it returns nil. In the present case
this will let the Octokit::Client object use whatever default value it
wants for the ssl option.

Fix Elastic::Indexer spec

This break was broken by !273.

See merge request !277

ES: Fix. bin/elastic_repo_indexer follows config

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/390

See merge request !276