Users can only view projects which they are associated with

[jgaskins]

• On the project index, users only see projects they are associated with
• On the project show page, users should be redirected to the index page unless they're associated with that project
• On the project edit page, if different from show, make sure they can't submit the form

Recommendation for the pundit gem, but if you have an alternate preference, we're open to suggestions. :-)

Depends on #61

[Diego-Thomaz]

I'd like to work on this one

[Diego-Thomaz]

Job's done.