manual sorting of commands and summaries

As discussed with @qwcode, the order of the commands shown by `pip --help` could be a bit more meaningful. 

Before:
```
Usage:   
  pip <command> [options]

Commands:   
  unzip                       Unzip individual packages.
  help                        Show help for commands.
  show                        Show information about installed packages.
  bundle                      Create pybundles.
  freeze                      Output installed packages in requirements format.
  search                      Search PyPI for packages.
  zip                         Zip individual packages.
  list                        List installed packages.
  install                     Install packages.
  uninstall                   Uninstall packages.
```

After:
```
Usage:   
  pip <command> [options]

Commands:   
  install                     Install packages.
  uninstall                   Uninstall packages.
  freeze                      Output installed packages in requirements format.
  list                        List installed packages.
  show                        Show information about installed packages.
  search                      Search PyPI for packages.
  zip                         Zip individual packages.
  unzip                       Unzip individual packages.
  bundle                      Create pybundles.
  help                        Show help for commands.
```