Create dev fixture projects with fixed visibility

Creates 3 new projects: one public, one private and one internal. For each project create a new user which is it's owner.

Really helpful to test cases things where visibility matter.

Factor out `Sidekiq::Testing.inline! do` into the `Seeder` with 04_projects.

Create a `fixtures_development_helper.rb` helper file because I am pretty sure that will be reused afterwards.
Prefer single-quoted strings when you don't need string interpolation or special symbols.