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

backend/cache/cache.go

@@ -1414,14 +1414,11 @@ func (f *Fs) CleanUp() error {
 }
 
 // About gets quota information from the Fs
-func (f *Fs) About() error {
-	f.CleanUpCache(false)
-
+func (f *Fs) About() (*fs.Usage, error) {
 	do := f.Fs.Features().About
 	if do == nil {
-		return nil
+		return nil, errors.New("About not supported")
 	}
-
 	return do()
 }