Scheduled weekly dependency update for week 26

Add VIT to known_chains

Missing Account import
Thank you for the correction!

Scheduled weekly dependency update for week 25

Discussions
* Examples added to all classes
* Discussions add for fetching more than 100 posts

estimate_virtual_op_count: avoid division by zero

Fixes #34

* "Bad or missing upstream response" is handled

Block
* switch to condenser when api call does not work on appbase node
* blocknum property returns Null when block is empty
Blockchain
* check improved in  threading blocks
Discussions
* set_next_node_on_empty_reply set to False
Steemnoderpc
* Request Timeout added
Unit tets
* test_account for appbase nodes improved

* stream_threading_performance example added to evaluate threading
* _switch_to_next_node added to Steemnoderpc
* 5 tags restriction removed from post()

move get_similar_account_names from Account to Blockchain + Wallet DRY
Thank you @crokkon for this PR, it looks good to me.

* consolidate / DRY
* update documentation

index.rst: fix blockchain example