Reset User.current in a "setup" phase

Resetting the User.current at the end of a test makes other tests break
if the former tests itself breaks. We could have a "ensure" phase in the
test but having a "setup" phase seems cleaner and easier to understand.
Explicitly declare needed fixtures so that the test can be run alone
Add some comments in test/functional/projects_controller_test.rb
Don't patch ProjectsController in test environment so that we don't break core tests
Don't use fixtures in functional tests

When we use specific fixtures for project queries, either we break core
tests, either we break this plugin test when running with all other
plugins tests.