Upgrade to alpha.5

[ETeissonniere]

Describe the enhancement
The last published version of substrate is 2.0.0-alpha.5, we should upgrade our node and runtime to keep up to date. Additionally this may include fixes useful for #28.

[ETeissonniere]

Talked to parity, they have decided to remove the migrations code and suggest running a new testnet

[ETeissonniere]

Holding until beta finalization