Initial Admin Access for Projects

This new feature allows one to set an initial access for admins when
creating a new project. The default choice can be set in
config/gitlab.yml, under 'default_project_access'. Cucumber test
included.

I welcome discussion around what the Gitlab team might actually want, related to this feature. For example:

* _all_ users instead of admins? Admins just worked for my team.
* different default, like 'none'?