Adding support for DNS _pka entries. Closes #522.
Make class naming intuitively illogical (issue #547)
Added support for "data views", implemented in demos.py (issue #547, issue #507)
1st draft of registering UI elements (issue #547)
Started work on leap plugin.

- Uses new plugin structure.
Removed soledad from mailboxes.
Renamed plugin to leap.
Added startup and shutdown to plugin manifests.
Removed sync from mailbox.unparsed.
Moved config fetch to provider.
Provide mailpile config as param to mailboxes.
Moved LeapSession to session.py.

- Removed unused code.
Added mocking tests for leap integration.
Moved leap session dependency creation to factory.