Enable history, autocomplete in shell task

I totally stole this from Django's
``django.core.management.commands.shell``.  I added a comment and
the Django license to specify this, but we might need to address
this in a different way if the licenses are incompatible.
Validators for 2008 Maryland elections

Contest, candidate and result count valdiators for the Maryland's
2008 primary and general elections.

Also add a transform to compress multiple rows of
"Uncommitted to Any Presidential Candidate" results in the
Democratic primary into a single result per legislative district.

Addresses https://github.com/openelections/core/issues/36