Allow 'Commands:' and 'Options:' line be longer, e.g.:
'Commands that only show information:' or
'Commands that manipulate with devices:'.
Reworked storage command docs.

- moved listing commands to the top.
- clearly split commands that only show/list devices from commands which
  modify devices.
- added short notice that LUKS means encryption.
Merge pull request #112 from jsafrane/devel/rtd

Storage doc changes