Initial project setup and skeleton (#4)

* initial project setup for beefy gadget client

* update editorconfig

* update gitignore

* add initial skeleton for beefy gadget worker

* add skeleton for gossip processing

* add app crypto

* move around some code

* add basic flow for voting

* add logic for picking blocks to sign

* add rustfmt config

* add example node with beefy gadget

* use u32::next_power_of_two

* make maximum periodicity configurable

* add copyright header

* rename max_periodicity to min_interval