[#613] Add media print stylesheet
Merge pull request #645 from jwaterfaucett/add_print_stylesheet

[#613] Add media print stylesheet
Made HTML-to-text results more readable, extracted links
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.
Started tests on LeapSession.
Moved leap requirements to leap plugin folder.
Added mock test for srp login.
Added session id verification to login test.
Added test for timeout handling.
Removed setUp from LeapTest.
Replaced provider test with mock test.