Upgrade for CKAN 2.11

[jonathansberry]

Description

Makes a number of changes required to get ckanext-dataset-subscriptions working with CKAN 2.11.

The activity features of CKAN have been moved from core to ckanext-activity which is shipped alongside core. The changes here update the code base to reflect this. They also simplify the user_edit form, taking advantage of form refactoring that has taken place upstream in CKAN core.

Checklist

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• The Jira ticket for this issue has been updated to "Ready to Review" or equivalent.
• I have developed these changes in discussion with the appropriate project manager.
• My code follows the general Fjelltopp documentation (see Confluence).
• I have made corresponding changes to the Fjelltopp documentation (see Confluence).
• I have rebased this branch with master.
• New dependency changes have been committed.
• I have added automated tests that prove my fix is effective or that my feature works.
• New and existing tests pass locally with my changes.
• My changes generate no new warnings.
• I have performed a self-review of my own code.
• I have assigned at least one reviewer.
• I have assigned at least one label to this PR: "patch", "minor", "major".

[ntwalibas]

LGTM