TEST.2.0

• main change: endorsement system, massively increasing architecture-based attack costs and making attack attempts fully prohibitive (see scientific paper)
• changed the block reward to 0.3 coins
• changed roll price to 100 coins per roll
• changed the periods_per_cycle parameter from the temporary debugging "10" value to the final "128" value, thus making cycles much longer and reducing the probability that a single miss causes an implicit roll sale
• config override: now, the massa-node/base_config (and massa-client/base_config) folder contains configuration files that shouldn't be edited by the user while massa-node/config (and massa-client/config) contain user-editable files that override the base config and also contain the node_privkey and staking_keys files. This makes massa docker-friendly.
• the massa-node/storage folder now contains all the storage data, in order to be container-friendly and pave the way to docker CD
• added warnings on misses and implicit roll sales happening on addresses staked by the node
• internal rework of the block_graph system to allow retrieving clique fitnesses after computation, and always knowing which clique is the blockclique
• various improvements on logging, UX, docs, performance and stability

Full Changelog: TEST.1.3...TEST.2.0