ISSUE-197 Create classes for OAuth Login providers

...ava/edu/kit/scc/webreg/entity/oauth/OAuthGroupEntity.java

...t/scc/webreg/entity/oauth/OAuthRpConfigurationEntity.java

...u/kit/scc/webreg/entity/oauth/OAuthRpFlowStateEntity.java

...java/edu/kit/scc/webreg/entity/oauth/OAuthUserEntity.java

...kit/scc/webreg/service/disco/DiscoveryCacheSingleton.java

...scc/webreg/service/oauth/OAuthRpConfigurationService.java

...breg/service/oauth/client/OAuthClientCallbackService.java

.../service/oauth/client/OAuthClientCallbackServiceImpl.java

...breg/service/oauth/client/OAuthClientRedirectService.java

.../service/oauth/client/OAuthClientRedirectServiceImpl.java

...it/scc/webreg/service/oauth/client/OAuthGroupUpdater.java

...c/webreg/service/oauth/client/OAuthUserCreateService.java

...kit/scc/webreg/service/oauth/client/OAuthUserUpdater.java

...eg/service/oidc/client/OidcClientCallbackServiceImpl.java

...eg/service/oidc/client/OidcClientRedirectServiceImpl.java

...n/java/edu/kit/scc/webreg/bean/RegisterOAuthUserBean.java

...ava/edu/kit/scc/webreg/bean/disco/DiscoveryLoginBean.java

...kit/scc/webreg/sec/OAuthClientCallbackHandlerServlet.java

...kit/scc/webreg/sec/OAuthClientRedirectHandlerServlet.java

.../src/main/java/edu/kit/scc/webreg/sec/SecurityFilter.java