Basic Asset Implementation

This PR implements the basic asset managment.

Currently there are 2 supported usecases:

# Standalone

For standalone you have to include ```Lotus::Assets::Helpers``` into your template objects class.
Also if you don't follow the conventions you have to configure ```Lotus::Assets``` via:

```ruby
Lotus::Assets.configure do
  assets_path 'assets'
  stylesheet_path 'stylesheets'
  javascript_path 'javascripts'

  path_prefix ''
  to_file true
end
```

Note: The options in the above configure block are the default values.

For further usage description in standalone mode look at the [example](https://github.com/bennyklotz/assets/tree/master/examples/standalone)

# Semi-standalone (with Lotus::View but not full-stack)

Also for the usage with ```Lotus::View``` you have to configure properly if not following the conventions and including ```Lotus::Assets::Helpers``` into the view class.

[Example](https://github.com/bennyklotz/assets/blob/master/examples/semi-standalone/semi-standalone.rb)

# Full-stack

Currently the full-stack mode doesn't differ from the others. This means you have to configure properly or following the default values. In future ```lotus/lotus``` will configure properly so you can include ```Lotus::Assets::Helpers``` into different views of different lotus applications without worrying about the configuration.

### Note:

This codebase serves as basic layout for the future and needs some heavy refactoring.