Redefine logical volume types.

Now we only have "blocks" and "pool", to reflect how a volume can be
used.
New "options" treatment in the D-Bus API.

- A "options" argument is now intended to pass additional options to
  the lvm2 commands that are spawned, and we only include it for
  operations that have a lot of options.  For example, Rename has no
  options anymore, but CreateThinVolume now has.

- Some arguments like extent size and stripe configuration
  should be done with options, but have been removed for now.

- The "wipe" option is now passed as a regular argument.