Migration jcrown

Opening this pull request for discussion and review purposes, there is still MUCH to be done!!!!

migration.py is a sample of how we can use the library to perform the actual migration
ftpmirror.py takes care of recursive download via FTP. It would probably make sense to organize it a little bit better (like putting it in a class), as well as adding a recursive upload method, which would allow us to upload the stuff to the destination server, hence avoiding the tarball (this seems pertinent since untarring might be a pain on some setups).

TODO's

MUCH more error checking!
search and replace of old file paths in files and database
separate the WP specific stuff from the general use stuff
figure out how to organize our plugin repo (see the plugin_update_jcrown branch for the source of the plugin), as of right now migration.py is just blindly assuming that the zip file for the plugin is in the same directory.
Possibly use MD5 has instead of file size to ensure that the downloaded file was not corrupted in any way.
There's no need to set the header each time, since it is saved into the session.