Improve & fix the performance bar UI and behavior

app/assets/javascripts/dispatcher.js

app/assets/javascripts/peek.js

app/assets/javascripts/performance_bar.js

app/assets/stylesheets/framework/modal.scss

app/assets/stylesheets/framework/variables.scss

app/assets/stylesheets/performance_bar.scss

app/helpers/nav_helper.rb

app/helpers/performance_bar_helper.rb

app/views/help/_shortcuts.html.haml

app/views/layouts/_head.html.haml

app/views/layouts/application.html.haml

app/views/peek/views/_rblineprof.html.haml

app/views/peek/views/_sql.html.haml

config/application.rb

config/webpack.config.js

lib/gitlab/performance_bar.rb

lib/peek/rblineprof/custom_controller_helpers.rb