add dictator.sol

[dkent600]

@orenyodfat @jellegerbrandy Would be great if docs like this could be in the code:

https://github.com/daostack/arc/pull/752#pullrequestreview-416941211

[orenyodfat]

• deploy our daos with the dictator scheme registered, and with dictator.owner set to 0xdaostack
• call dictator.registerScheme(0xdaostack)
• and now we can do everything the controller allows us to do from the 0xdaostack account

not exactly :

• The owner of dictator is 0xdaostack .
• 0xdaostack can register any arbitrary scheme or account with full permission to the dao by calling call dictator.registerScheme(0xanyarbitraryschemeoraccount)

0xanyarbitraryschemeoraccount can do what ever.

changing ownership of Dictator will be 1 step :

• dictator.transferOwnership(0xnewOwner)

Such a contract is needed to register 0xanyarbitraryschemeoraccount due to the fact that daoFactory can register contracts only.