PLT-1316/PLT-3280 Change client-side max file size limit (#3354)

* Change client-side max file size limit

It now relies on the value set in config.json.
Re-enable and tweak the max file size setting in system console.

* Update file upload error message

webapp/utils/constants.jsx

@@ -210,7 +210,6 @@ export default {
     },
     MAX_DISPLAY_FILES: 5,
     MAX_UPLOAD_FILES: 5,
-    MAX_FILE_SIZE: 50000000, // 50 MB
     THUMBNAIL_WIDTH: 128,
     THUMBNAIL_HEIGHT: 100,
     WEB_VIDEO_WIDTH: 640,