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/hooks/toast.ts

@@ -0,0 +1,16 @@
+import { useDispatch } from "react-redux"
+import { setMessage } from "../features/ui/toastSlice"
+import { AlertColor } from "@mui/material"
+
+export const useToast = () => {
+  const dispatch = useDispatch()
+
+  return {
+    pushMessage: (message: string, severity?: AlertColor) => {
+      dispatch(setMessage({
+        message: message,
+        severity: severity
+      }))
+    }
+  }
+}