added icons and fixed mini pipeline action dropdown icons

app/assets/stylesheets/pages/pipelines.scss

app/views/ci/status/_dropdown_graph_badge.html.haml

app/views/ci/status/_graph_badge.html.haml

app/views/shared/icons/_icon_action_cancel_borderless.svg

app/views/shared/icons/_icon_action_play_borderless.svg

app/views/shared/icons/_icon_action_retry_borderless.svg

app/views/shared/icons/_icon_action_stop_borderless.svg

lib/gitlab/ci/status/build/cancelable.rb

lib/gitlab/ci/status/build/play.rb

lib/gitlab/ci/status/build/retryable.rb

lib/gitlab/ci/status/build/stop.rb