Elfinder connector route. Rails 4 support

Those are small additions to my previous PR. 

1. I replaced `:elfinder` with `'elfinder'` because it caused an error during installation, in `rails 4` app.

```
➜  myapp git:(admin_products) ✗ rails generate elrte:install
       route  Elrte.routes(self)
    generate  elrte:assets
/Users/vlad/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0.rc1/lib/action_dispatch/routing/mapper.rb:229:in `default_controller_and_action': missing :controller (ArgumentError)
  from /Users/vlad/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0.rc1/lib/action_dispatch/routing/mapper.rb:116:in `normalize_options!'
  from /Users/vlad/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0.rc1/lib/action_dispatch/routing/mapper.rb:64:in `initialize'
................
  from /Users/vlad/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0.rc1/lib/action_dispatch/routing/mapper.rb:557:in `get'
  from /Users/vlad/Ruby/elrte-rails/lib/elrte/router.rb:17:in `apply'
  from /Users/vlad/Ruby/elrte-rails/lib/elrte/application.rb:11:in `routes'
  from /Users/vlad/Ruby/elrte-rails/lib/elrte.rb:23:in `routes'
  from /Users/vlad/Ruby/myapp/config/routes.rb:3:in `block in <top (required)>'
.......
```

2. Also I set it back to use `match`, but in `rails 4` way using `:via` to specify http methods explicitly.