Port people search to Bootstrap

This was part of #4657 which might take a while. 

I moved the files for blueprint invitations and added new ones for Bootstrap invitations. Once the stream has been ported to Bootstrap one could remove the old blueprint invitation files.

![people search](https://cloud.githubusercontent.com/assets/3798614/3635020/510e1746-0f58-11e4-90fa-8bc44555659c.png)

![invitation](https://cloud.githubusercontent.com/assets/3798614/3635022/6e0c969c-0f58-11e4-90dd-bfefd7169cd6.png)
I don't like that this is duplicating the above action exactly. I see two possibilities here

```ruby
def new(view = 'invitations/new')
 ...
    render view, layout: false
end

def new_blueprint
  new 'invitations/new_blueprint'
end
```

Or passing a parameter `?blueprint=true` instead of changing the path to `new_blueprint` and then

```ruby
def new
...
  render params[:blueprint] ? 'invitations/new_blueprint' : 'invitations/new', layout: false
```

I think I slightly prefer the second option.