Add theme browser page accessible from game options

Removed the themes buttons that were in the ThemeEditorModal and only
left a "Revert to Default" button along with a link to the ThemeBrowser
page.

Split off the buttons into reusable components since they are now used
in two pages.

Display the themes in big cards with a zoomable screenshot. Applying the
theme now shows a toast with an option to undo the action.

The snackbar now allows ReactNode instead of only strings.

- Add link with details on how to create a new theme in the game.
- Add link to the theme-sharing discord channel.
- Add icons to the theme & style buttons in GameOptions
- Add "Theme Editor" button to ThemeBrowser
- Add "Style Editor" button to ThemeBrowser
- Move Styles related files into Themes folder
- Includes a modal that shows a bigger version of the screenshot.
- Change Snackbar to allow for ReactNode as the message

src/ui/React/Snackbar.tsx

@@ -14,6 +14,10 @@ const useStyles = makeStyles(() => ({
   snackbar: {
     // Log popup z-index increments, so let's add a padding to be well above them.
     zIndex: `${logBoxBaseZIndex + 1000} !important` as any,
+
+    "& .MuiAlert-icon": {
+      alignSelf: 'center',
+    },
   }
 }));
 
@@ -27,7 +31,7 @@ export function SnackbarProvider(props: IProps): React.ReactElement {
   );
 }
 
-export const SnackbarEvents = new EventEmitter<[string, "success" | "warning" | "error" | "info", number]>();
+export const SnackbarEvents = new EventEmitter<[string | React.ReactNode, "success" | "warning" | "error" | "info", number]>();
 
 export function Snackbar(): React.ReactElement {
   const { enqueueSnackbar, closeSnackbar } = useSnackbar();