Add parameters before_filter and fallback_to_devise

Commit makes before_filters are optional
- `before_filter` - disables all before_filters
- `fallback_to_devise` - disables `before_filter :authenticate_entity!`

Example of usage:
```ruby
class HomeController < ApplicationController
  acts_as_token_authentication_handler_for User, before_filter: false

  before_filter :authenticate_entity_from_token!, only: :destroy

  def index
    # ... Accessible for unauthenticated users ...
  end

  def destroy
    # ... Only for authenticated users...
  end
end
```