- fixes issue #122 - delete group only if group has no exercises

i18n/en.ts

i18n/i18nRoot.ts

src/communicationLayer/exercisesOverviewLayer.ts

src/communicationLayer/genericLayer.ts

src/communicationLayer/groupsLayer.ts

src/communicationLayer/testingLayer.ts

.../afterCustomTestsPanel/afterCustomTestsPanelHeaderBar.tsx

...erciseSite/customTestsPanel/customTestsPanelHeaderBar.tsx

.../doExerciseSite/customTestsPanel/customTestsPanelView.tsx

src/components/sites/groupsSite/groupsListView.tsx

...oupExerciseComponents/submissionsSite/submissionsSite.tsx

...nents/sites/systemSettingsSite/testServerSettingsView.tsx

...orViewSite/normalTestsPanel/normalTestsPanelHeaderBar.tsx

...orViewSite/submitTestsPanel/submitTestsPanelHeaderBar.tsx

src/constants.ts

...e/actions/exerciseEditorSite/exerciseEditorSiteActions.ts

...state/actions/groupsSite/dialog/groupDialogCrudActions.ts

src/state/actions/groupsSite/dialog/groupSetActions.ts

src/state/actions/groupsSite/groupsCrudActions.ts

src/state/actions/groupsSite/groupsSiteActions.ts