integrations: refactor/cleanup + features, fixes #4181 * added scopes on integrations, scopes are: - repo only - repogroup children only - root repos only - global (any repo) * integrations schemas now have separate section for the settings (eg. slack) and options (eg. scope/enabled) * added descriptions to integration types * added icons to integration types * added 'create new' integration page * added scope of integration to integrations list * added breadcrumbs for each repo/repogroup/global integrations pages * added sorting to integrations list * added pagination to integrations list * added icons to integrations list * added type filter to integrations list * added message to integrations list if none we found * added extra permissions check on integrations views * db migration from 56 => 57 - adds child_repos_only field * added tests for integrations triggered on events * added tests for integrations schemas * added tests for integrations views for repo/repogroup/admin