[Feature Request] Add semantic ui framework

Hi

[Semantic UI](https://semantic-ui.com/) is a popular frontend framework. Installing it is as simple as adding the following lines:

```ruby
#Gemfile
gem 'rails-assets-semantic', source: 'https://rails-assets.org'
```

```js
// application.js
//= require semantic
```

```css
/* application.css*/
 *= require semantic
```