GitLab

Changes:

• Add notifications system to hived. Thanks to this enchantment it's possible to send any info from application to any given endpoints via HTTP method (PUT).
• Add flag --list-plugins which prints names of all available plugins

Minor changes:

• Move test of hived behavior on unsupported plugin request from TestTools to hived
• Cleanup python_tests/cli_wallet/conftest.py and python_tests/hived/test_hived_options.py
• Update TestTools' logger configuration

Possible usage of notifications:

• monitoring state of hived (replaying, producing block, shutting down, etc.)
• alternative form of broadcasting statistics (currently only via JSON)
• alerting about on-chain assertions
• easier way for plugins to broadcast some information outside (ex. usage in AH [not implemented, just suggestion]: subscribe for some account and get all updates via this system, so there is no need to constantly ask for blocks)

Corresponding merge request in TestTools: test-tools!19 (merged)

@pbatko @bwrona @gandalf