Oasis Nexus 0.1.9

This is a bugfix release. Block 854327 in emerald mainnet is subject to the bug fixed in #497.

What's Changed

Bugfixes:

• update total_supply to accept negative updates by @Andrew7234 in #494
• bugfix: initialize possibleToken fields by @Andrew7234 in #497

Internal:

• pogreb: non-blocking recovery by @ptrus in #486
• add index for chain.addres_preimages.address_data by @Andrew7234 in #498

Full Changelog: v0.1.8...v0.1.9