extended execution environments by a default file type that is used as the default for associated exercises' files

app/views/execution_environments/_form.html.slim

@@ -3,6 +3,9 @@
   .form-group
     = f.label(:name)
     = f.text_field(:name, class: 'form-control', required: true)
+  .form-group
+    = f.label(:file_type_id)
+    = f.collection_select(:file_type_id, FileType.all.order(:name), :id, :name, {include_blank: true}, class: 'form-control')
   .form-group
     = f.label(:docker_image)
     |  

app/views/execution_environments/show.html.slim

@@ -4,6 +4,7 @@ h1
 
 = row(label: 'execution_environment.name', value: @execution_environment.name)
 = row(label: 'execution_environment.user', value: link_to(@execution_environment.author, @execution_environment.author))
+= row(label: 'execution_environment.file_type', value: @execution_environment.file_type.present? ? link_to(@execution_environment.file_type, @execution_environment.file_type) : nil)
 - [:docker_image, :exposed_ports, :permitted_execution_time, :pool_size, :run_command, :test_command].each do |attribute|
   = row(label: "execution_environment.#{attribute}", value: @execution_environment.send(attribute))
 = row(label: 'execution_environment.testing_framework', value: @testing_framework_adapter.try(:framework_name))