[#6480] Improvements to Trac importer

- Disable email notifications during import
- Retry time-out HTTP requests
- Add option to supply user-map file

Signed-off-by: Tim Van Steenburgh <tvansteenburgh@gmail.com>
[#6506] Add custom User-Agent and auto-retries for project export requests

Signed-off-by: Tim Van Steenburgh <tvansteenburgh@gmail.com>
[#6506] Minor mocking cleanup

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#6506] Shortened Trac Ticket Importer tool_label

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#6506] Fixed unicode and attribute errors

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#6506] Added TracWikiImporter to requirements-sf.txt

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>