Move "Add new Project" button to header

Since we are not paginating the full list of projects, the button being
below the list of projects could potentially become a problem when you
have a large list of projects. Moving it to the top header resolves
that.
Remove bad assertion from projects controller spec

I removed edit links from the projects index page in commit
2a11c61db01115 but forgot to update specs. This addresses that by
removing an assertion that was no longer true. I double checked that the
`#show` spec was already verifying that the edit link was there.