[Delivers #45975387] Show warning when bronze browser detected

Add a browser check when a user first accesses the application and determine whether the support is :bronze, :silver, :gold or :unknown - show a message if a :bronze or :unknown.

This pulls in a new gem 'useragent' which allows easy parsing of the agent string and comparison helpers.

Also remove the 'markaby' gem as we don't seem to use it anywhere.