Added small improvments to the chat slash command services

app/assets/stylesheets/framework/lists.scss

app/models/project_services/chat_slash_commands_service.rb

...els/project_services/mattermost_slash_commands_service.rb

app/models/project_services/slack_slash_commands_service.rb

...rvices/mattermost_slash_commands/_detailed_help.html.haml

...ojects/services/mattermost_slash_commands/_help.html.haml

...ws/projects/services/slack_slash_commands/_help.html.haml

doc/user/project/integrations/img/mattermost_config_help.png

doc/user/project/integrations/img/slack_setup.png

...atures/projects/services/mattermost_slash_command_spec.rb

spec/features/projects/services/slack_slash_command_spec.rb