Replace cultivar_name with cultivar. Fixes #58.
Native status is now nullable boolean. Fixes #90.
Reputation is tied to an instance, it cannot be null.

Fixes #168
Implement popstate event for history tracking

Fixes #190
Conditionally hide private instance audits. Fixes #184.

Previously the user page (which is global) showed recent edits for all
instances. Now recent edits will include only:

* Public Instances
* Instances that the current view has access to
Allow deleting users. Fixes #117

The audit framework assumed that auditable objects have an 'instance'
param, which is not always the case.
Merge pull request #192 from ahinz/topic/random-fixes

Topic/random fixes