Refactor: every command is represented by a class

Works only VPS start/stop/restart.
Gemfile: add require_all
Commands register themself using handle method
Command: fix handling of a bad return value from transaction
Use class dataset
Shaper: use method arguments instead of @params
Node: add method conf_path
Vps: adapt create, ip add/del, applyconfig, add ve_private_ds
Add command Dataset::Create
Add command Dataset::Destroy
ADd command Vps::ApplyConfig
Add commands Vps::Create and Vps::Destroy
Add commands Vps::IpAdd and Vps::IpDel
Refactor: move classes to module VpsAdmind