Factor Maryland jurisdiction lists to separate module

Move county and congressional district lists to
``openelex.us.md.jurisdiction`` instead of being a class attribute
of an ad-hoc class in ``us.md.validate``.

Addresses https://github.com/openelections/core/issues/104
Validate 2000 general election result counts

Add state legislative districts to ``us.md.jurisdiction``.

Add ``election_id`` attribute to election description class and
change functon signatures to use this attribute rather than passing
the election id explicitely.

Validate the number of results on a reporting level basis.

Reorganize the code, grouping helper functions, election-specific
validators, and general validators.

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