about: complete other providers and re-work internals

* Implement about for:
    * local, crypt, cache, drive, swift, hubic, onedrive, pcloud, dropbox
  * Implement `--json` and `---full` flag for `rclone about`
  * change About interface to return a Usage structure
  * Remove operations.About as it is too thin an interface
  * Implement Integration test

Relates to #1138 and #1564

fs/operations/operations.go

@@ -1049,19 +1049,6 @@ func CleanUp(f fs.Fs) error {
 	return doCleanUp()
 }
 
-// About gets quota information from the remote
-func About(f fs.Fs) error {
-	doAbout := f.Features().About
-	if doAbout == nil {
-		return errors.Errorf("%v doesn't support about", f)
-	}
-	if fs.Config.DryRun {
-		fs.Logf(f, "Not running about as --dry-run set")
-		return nil
-	}
-	return doAbout()
-}
-
 // wrap a Reader and a Closer together into a ReadCloser
 type readCloser struct {
 	io.Reader