Replace bootstrap caret with fontawesome caret

CHANGELOG

app/assets/javascripts/pipeline.js.es6

app/assets/stylesheets/framework/buttons.scss

app/assets/stylesheets/framework/dropdowns.scss

app/assets/stylesheets/framework/forms.scss

app/assets/stylesheets/framework/header.scss

app/assets/stylesheets/framework/selects.scss

app/assets/stylesheets/pages/pipelines.scss

app/views/dashboard/todos/index.html.haml

app/views/explore/groups/index.html.haml

app/views/explore/projects/_filter.html.haml

app/views/layouts/header/_default.html.haml

app/views/projects/branches/index.html.haml

app/views/projects/ci/pipelines/_pipeline.html.haml

app/views/projects/commit/_commit_box.html.haml

app/views/projects/commit/_pipeline.html.haml

app/views/projects/deployments/_actions.haml

app/views/projects/forks/index.html.haml

app/views/projects/group_links/index.html.haml

app/views/projects/issues/show.html.haml