Download REST API endpoints (#72)

* backend and frontend hotfixes, see message

Improved rendering on the frontend by cutting unecessary useStates.
Backend side, downloads now auto resume even on application kill.

* download rest api endpoints, general code refactor

* download request json mappings

frontend/src/providers/ToasterProvider.tsx

@@ -0,0 +1,23 @@
+import { Alert, Snackbar } from "@mui/material"
+import { useDispatch, useSelector } from "react-redux"
+import { setClose } from "../features/ui/toastSlice"
+import { RootState } from "../stores/store"
+
+const Toaster: React.FC = () => {
+  const toast = useSelector((state: RootState) => state.toast)
+  const dispatch = useDispatch()
+
+  return (
+    <Snackbar
+      open={toast.open}
+      autoHideDuration={toast.severity === 'error' ? 10000 : 1500}
+      onClose={() => dispatch(setClose())}
+    >
+      <Alert variant="filled" severity={toast.severity}>
+        {toast.message}
+      </Alert>
+    </Snackbar>
+  )
+}
+
+export default Toaster