Planetmint

* **fixed** inconsistent cryptocondition keyring tag handling. Using cryptoconditions > 1.1.0 from now on.

* **Added** added upgrade compatibility to older nodes to support v2.0 TX validity for nodes supporting v3.0 transactions (planetmint-transactions >= 0.4.1)

* **Changed** new zenroom 2.3.1 support
* **Changed** integrated new planetmint-cryptoconditions package (via the transactions package)

Added
* Metadata full-text search. [Pull request 1812](https://github.com/planetmint/planetmint/pull/1812)

Notes
* Improved documentation about blocks and votes. [Pull request 1855](https://github.com/planetmint/planetmint/pull/1855)

* **Changed** A connection singleton got introduced to avoid connection issues and unstable states.