Light related methods is moved from Client class to Bridge class.

The light of all the bridges can be operated as follows.

```ruby
require 'hue'
client = Hue::Client.new

lights = client.bridges.map { |bridge| bridge.lights }.flatten

lights.each do |light|
  light.on = true
  light.saturation = 180
  light.brightness = 200
  light.hue = 14922
end
```