Include PF4 styles for settings page

[damianpm]

What this PR does / why we need it:
The new integration settings component #1315 is missing PF4 styles.
Since #1019 we should import explicitly all PF4 styles required. This was a recommendation from PF4 team: https://github.com/patternfly/patternfly-react-seed/wiki/Disable-Patternfly-React-Auto-Style-Injection.

Which issue(s) this PR fixes

https://issues.jboss.org/browse/THREESCALE-3563

Verification steps

run bundle exec rake webpack:compile && bundle exec rake assets:precompile

Special notes for your reviewer:
Apply this patch to make it work:

diff --git a/app/javascript/packs/settings.js b/app/javascript/packs/settings.js
index e9bb1a69..0bfeb4b6 100644
--- a/app/javascript/packs/settings.js
+++ b/app/javascript/packs/settings.js
@@ -1,5 +1,5 @@
-import { initialize as authenticationWidget } from 'Settings/authentication-widget'
+import { initSettings as settingsWidgets } from 'Settings/index'

 document.addEventListener('DOMContentLoaded', () => {
-  authenticationWidget()
+  settingsWidgets({elementId: 'settings'})
 })

[codecov]

Codecov Report

Merging #1402 into THREESCALE-3563/integration-settings will increase coverage by 16.86%.
The diff coverage is n/a.

@@                            Coverage Diff                            @@
##           THREESCALE-3563/integration-settings    #1402       +/-   ##
=========================================================================
+ Coverage                                 75.95%   92.81%   +16.86%     
=========================================================================
  Files                                      1799     2443      +644     
  Lines                                     51196    80397    +29201     
=========================================================================
+ Hits                                      38886    74622    +35736     
+ Misses                                    12310     5775     -6535

Impacted Files	Coverage Δ
...sks/data_migration/fix_backend_config_path_test.rb	100% <0%> (ø)	⬆️
test/unit/tasks/swagger_test.rb	100% <0%> (ø)	⬆️
test/unit/tasks/sidekiq_test.rb	100% <0%> (ø)	⬆️
test/unit/stats/base_test.rb	100% <0%> (ø)	⬆️
test/unit/tasks/impersonation_admin_user_test.rb	100% <0%> (ø)	⬆️
test/unit/tasks/forum/migrate_forum_test.rb	100% <0%> (ø)	⬆️
test/unit/tasks/cms/cms_test.rb	100% <0%> (ø)	⬆️
spec/acceptance/api/feature_spec.rb
...n/user/notification_preferences_controller_test.rb	100% <0%> (ø)
...st/workers/delete_account_hierarchy_worker_test.rb	100% <0%> (ø)
... and 1364 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 441075d...05220ea. Read the comment docs.