Refactor bucket delete and bucket policy (#5580)

This commit adds the bucket delete and bucket policy functionalities
to the browser.

Part of rewriting the browser code to follow best practices and
guidelines of React (issues #5409 and #5410)

The backend code has been modified by @krishnasrinivas to prevent
issue #4498 from occuring. The relevant changes have been made to the
code according to the latest commit and the unit tests in the backend.
This commit also addresses issue #5449.

browser/app/js/objects/actions.js

@@ -58,7 +58,8 @@ export const fetchObjects = append => {
       buckets: { currentBucket },
       objects: { currentPrefix, marker }
     } = getState()
-    return web
+    if (currentBucket) {
+      return web
       .ListObjects({
         bucketName: currentBucket,
         prefix: currentPrefix,
@@ -87,6 +88,7 @@ export const fetchObjects = append => {
         dispatch(alertActions.set({ type: "danger", message: err.message }))
         history.push("/login")
       })
+    } 
   }
 }