Store and load the blockchain from a file

[JeremyPansier]

Context
Verifying the whole blockchain might take more time as it grows up.

Description
A lot of time can be saved if the blockchain can be stored into a file to be loaded the next time the node is started.

Tasks
Try to split the feature into small tasks.

• Make it possible to store the blockchain into a file
• Make it possible to load the blockchain from a file

[JeremyPansier]

The registered addresses and the wallet balances should be stored too.

[JeremyPansier]

The added and removed registered addresses should be store in the block this way:
3b9e924#diff-bf087bbb04af5e09dc6414f3eb451376375ae0defbf767a6c60cc2190d18d4ecR52

But this is not verifiable until the node stores a list of registered addresses. Paradoxically, the changes above might be useless when a list of registered addresses is stored.