Internally public projects

Public projects listed in the public section will be linked to the actual project's page. Public projects now give any user Guest permissions to the project, allowing them to download the code, read and create issues, and view anything else in the project's pages.

Ample access tests have been added to the project_access_spec to verify correct permissions and behavior on public projects.
- Visitors to the site who are not logged in still cannot view the project's pages.
- Logged-in users visiting a public project where they are not a team member can create issues, but not snippets. They can view the projects code, issues, merge requests, etc, just as if they were a Guest member of the project.
- Since this is a public project, the user is also granted :download_code permissions, a permission normally reserved for Reporters, since they can clone the repo anyways and browse commits and branches locally.

This pull request is related to http://feedback.gitlab.com/forums/176466-general/suggestions/3159951-allow-public-repositories and http://feedback.gitlab.com/forums/176466-general/suggestions/3776706-allow-internal-open-public-repositories

Public Area with project names as links:
![screen shot 2013-05-02 at 12 17 37 am](https://f.cloud.github.com/assets/689175/452708/658d9092-b2f8-11e2-8162-94c7ba5a17bf.png)