Improve the efficiency of user_show

Instead of returning up to 50 of the datasets that a user can administer
now the call must specify that it wants those datasets by passing in
```include_datasets:True```.

The num_followers value must also be explicitly requested in order to be
included in the resulting dict.

Revisions are no longer returned, users should call user_activity_list
instead.

fixes #2130
[#2130] Do not list a users deleted or private datasets. Tightened up docs a little.
[#2130] Decided to exclude private datasets from the number a user created.
[#2130] Added details of the returned dictionary for user_show.
Merge branch '2130-user-show-slowness'