Improvements
- Support the hashing of `uuid.UUID` types by registering a hashing function [[1861]](https://github.com/aiidateam/aiida-core/pull/1861)
- Add documentation on plugin cutter [[1904]](https://github.com/aiidateam/aiida-core/pull/1904)
Minor bug fixes
- Make exported graphs consistent with the current node and link hierarchy definition [[1764]](https://github.com/aiidateam/aiida-core/pull/1764)
- Fix link import problem under SQLA [[1769]](https://github.com/aiidateam/aiida-core/pull/1769)
- Fix cache folder copying [[1746]](https://github.com/aiidateam/aiida-core/pull/1746) [[1752]](https://github.com/aiidateam/aiida-core/pull/1752)
- Fix bug in mixins.py when copying node [[1743]](https://github.com/aiidateam/aiida-core/pull/1743)
- Fix pgtest failures (release-branch) on travis [[1736]](https://github.com/aiidateam/aiida-core/pull/1736)
- Fix plugin: return testrunner result to fail on travis, when tests don't pass [[1676]](https://github.com/aiidateam/aiida-core/pull/1676)
Miscellaneous
- Remove pycrypto dependency, as it was found to have sercurity flaws [[1754]](https://github.com/aiidateam/aiida-core/pull/1754)
- Set xsf as default format for structures visualization [[1756]](https://github.com/aiidateam/aiida-core/pull/1756)
- Delete unused `utils/create_requirements.py` file [[1702]](https://github.com/aiidateam/aiida-core/pull/1702)