support any file source for any import type

Remove the restriction that flare imports are zips, and xml imports are
local files.
allow there to be no overriding settings

handle the case where no settings are there to override what's in the
plugging settings page
XML import works with zip file uploads

requires that the index.xml be at the root of the zip, but now can
upload a zip of the import using an index.xml index.
Merge pull request #34 from droppedbars/development

Support mix of file sources and import types