Feature/streamline backend requests (#297)

* Introduce "RequestManager"

* Use "RequestManager" - Simple replacements

 - Get rid of all "util/client" imports
 - replace old requests with new "RequestManager"
 - remove "fetcher" from global SWR config
     instead of using the SWR hooks by themselves, the "requestManager" is supposed to be used

* Use "RequestManager" - Do requests via SWR hooks

Use SWR hooks at places where it's easily usable

* Prevent trailing slashes in the "baseUrl"

src/components/context/AppContext.tsx

@@ -14,7 +14,6 @@ import { BrowserRouter as Router, Route } from 'react-router-dom';
 import { SWRConfig } from 'swr';
 import createTheme from 'theme';
 import { QueryParamProvider } from 'use-query-params';
-import { fetcher } from 'util/client';
 import useLocalStorage from 'util/useLocalStorage';
 import DarkTheme from 'components/context/DarkTheme';
 
@@ -36,7 +35,7 @@ const AppContext: React.FC<Props> = ({ children }) => {
     const theme = useMemo(() => createTheme(darkTheme), [darkTheme]);
 
     return (
-        <SWRConfig value={{ fetcher }}>
+        <SWRConfig>
             <Router>
                 <StyledEngineProvider injectFirst>
                     <ThemeProvider theme={theme}>