Added version 3 of time series file format

Version 3 of time series file format includes information about the
location to which the time series refers. It also has more relaxed
rules for its header.
Fix reading time series from SimpleUploadedFile

When uploading a time series to Enhydris, the file object is a
django.core.files.uploadedfile.SimpleUploadedFile object. This did not
work very well, at least not during unit testing. These changes (in
combination to related changes in Enhydris) fix the problem.
bitia now works locally with files

bitia does not communicate with Enhydris any more, but gets its input
from local files. A new application, pond, will soon be created that
will perform the communication with Enhydris and download updates to
local time series files. It will normally be run before bitia.