Add devise

Implemented authentication with devise.  Resolves all items in issue #4 as well as item 3 on issue #1 and item 3 on issue #2.
I would modify this to check to see if the food truck exists before creating it again. You can try finding the food truck by name and then updating it:

```ruby
food_trucks.each do |info|
  if !FoodTruck.exists?(info)
    FoodTruck.create!(info)
  end
end
```