Add project approval

##### A first stab at project submission (issue #107) that:
+ Adds new projects (and their organizations) as unapproved
+ Keeps unapproved projects (and their organizations) from appearing on site
+ Allows admins to approve projects

*ActiveAdmin approval checkbox*
![image](https://f.cloud.github.com/assets/2766324/1823152/f69e8c96-7173-11e3-86dc-60a40d7954ef.png)

*ActiveAdmin approval on show page*
![image](https://f.cloud.github.com/assets/2766324/1823185/f03fcec2-7174-11e3-99d1-890b4547bdf5.png)

*For implementation, it will need some minimal work in the console to update existing projects:*
```ruby
projects = Project.all
projects.each do |p|
  p.is_approved = true
  p.save!
end
```