This commit includes:

- Moved a lot of logic out of admin/users/add.php to the various plugins
- Moved around unzipping and detecting files into the transport layers
- Refactored a lot of transport code into the base class

I tested:

- Adding a user from a leap2a xml file
- Adding a user from a leap2a zip file
- Importing non leap (straight files) data over mnet

Signed-off-by: Penny Leach <penny@mjollnir.org>