dev_env_or_com? now considers dev.gitlab.org

Direct disk access is impossible on environments where components run in
their own container. There for constructing the path should not be done
except for exceptional cases.

One of the considerations, instead of logging, was to use Sentry. For
now I've chosen not to use this as the impact of this change is hard to
determine. Getting this in now will allow us to checkout the impact on
dev.gitlab.org and staging.

For quicker access, add hyperlink to the gitlab.com commits page for the current
REVISION of GitLab.

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

- Fix naming of API::CommitStatuses
- Ensure we use require_dependency instead of require
- Ensure the namespace is right in lib/api/api.rb, otherwise, we
  might require Grape::API::Helpers which defines the `#params` method.
  This is to avoid requiring a file multiple times and getting an "Already
  initialized constant" error.

Signed-off-by: Rémy Coutable <remy@rymai.me>

To be used as a feature flag for GitLab.com-only features, such as
welcome emails.

We will be careful to only use this to disable features or functionality
that do not make sense for any installations that aren't GitLab.com. We
will not use this to restrict features from other installations or keep
them "exclusive" to GitLab.com.

This reverts commit 5daf44b7, reversing
changes made to 2f706fbd.

This reverts commit 957e849f, reversing
changes made to 6b9dbe9f.

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