- fixes issue #89 - delete plang

...rSite/exerciseSettingsPanel/exerciseSettingsPanelView.tsx

...components/sites/systemSettingsSite/plangSettingsView.tsx

src/constants.ts

...ate/reducers/plangSettingsView/crud/createPLangReducer.ts

src/state/reducers/plangSettingsView/pLangsReducer.ts

src/types/pLangs.ts