Virtual-Ops support added for block and blockchain. Comment improved. More CLI functions.

Account
* estimate_account_op renamed to estimate_virtual_op_num
Block
* only_ops and only_virtual_ops added as new parameter
* the transactions property returns a list of transactions
* The operations property returns a list of operations
* Block which contain only only_ops can be received now
Blockchain
* only_ops and only_virtual_ops added to get_current_block, blocks, wait_for_and_get_block and stream
* ops() is obsolete now
* stream uses now blocks internally
* only_ops=True streams now also virtual operaitons
cli
* autoconnect is the to False now and only when needed a  stm.rpc.rpcconnect() is performed
* ascii option added to all plots
* rewards added, this new command lists outstanding rewards (posts, comment and votes)
* curation added which shows the vote curation rewards for a single post
* verify added, which returns the public signing key of a transaction
Comment
* reward, is_pending, time_elapsed, curation_penalty_compensation_SBD, estimate_curation_SBD, curation_reward_pct, get_vote, get_beneficiaries_pct, get_rewards, get_author_rewards and get_curation_rewards added

Unit tests
* new function added and tests adapted to changes