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/SourceCard.tsx

@@ -16,9 +16,9 @@ import { Box, styled } from '@mui/system';
 import React from 'react';
 import { useTranslation } from 'react-i18next';
 import { Link, useHistory } from 'react-router-dom';
-import useLocalStorage from 'util/useLocalStorage';
 import { ISource } from 'typings';
 import { translateExtensionLanguage } from 'screens/util/Extensions';
+import requestManager from 'lib/RequestManager';
 
 const MobileWidthButtons = styled('div')(({ theme }) => ({
     display: 'flex',
@@ -51,9 +51,6 @@ const SourceCard: React.FC<IProps> = (props: IProps) => {
 
     const history = useHistory();
 
-    const [serverAddress] = useLocalStorage<String>('serverBaseURL', '');
-    const [useCache] = useLocalStorage<boolean>('useCache', true);
-
     const redirectTo = (e: any, to: string) => {
         history.push(to);
 
@@ -86,7 +83,7 @@ const SourceCard: React.FC<IProps> = (props: IProps) => {
                                 flex: '0 0 auto',
                                 mr: 2,
                             }}
-                            src={`${serverAddress}${iconUrl}?useCache=${useCache}`}
+                            src={requestManager.getValidImgUrlFor(iconUrl)}
                         />
                         <Box
                             sx={{