Load config from backend API

The configuration is loaded at application initialization provided via
the new ApiConfigService. It includes properties for authentication
providers, feature settings and UI settings.

Refs arsnova-backend!161.
5 jobs for api-config in 8 minutes and 5 seconds (queued for 3 seconds)
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  Codestyle
passed #169028
nodejs
tslint

00:01:44

 
  Test
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nodejs
unit_tests

00:01:48

 
  Build
passed #169030
angular
ngbuild

00:04:31

 
  Review
canceled #169031
nginx
review

failed #169032
nginx allowed to fail manual
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