Move elections method implementation to BaseDatasource

The datasource ``elections()`` method had the same implementation,
which pulled elections from the metadata API, for a number of states.
It made sense to move this to the BaseDatasource class because I
can't imagine many situations where this implementation won't be
appropriate for other states.

I also created an election slug generation function,
``openelex.lib.text.election_slug`` and call it from
``BaseDatasource._election_slug()``.  This allows us to change
things in one place if we ever change our slug format.  However,
it might make

Finally, I cleaned up unused imports in the various state
datasource modules.

Closes https://github.com/openelections/core/issues/129
added beginnings of OH loader
Merge branch 'dev' of github.com:openelections/core into dev
updated requirements
fixed gov office slug in oh url_paths
Add notes field to result model

Also add transforms to set the notes field for Maryland
precinct-level results and update Maryland validators to
check sub-racewide totals against election day totals instead of
total totals.

Addresses https://github.com/openelections/core/issues/130,
https://github.com/openelections/core/issues/123
Update logic for registering transform functions
Update bulk transform syntax

Addresses https://github.com/openelections/core/issues/130
fixed date formatting for wv url_paths
fetch pre-2008 WV files from github repo
WV csvs do not have winner flag
added pre_processed_url to datasource attrs
Merge branch 'dev' into 125-raw_fetch
s/raw/unprocessed/

Use "unprocessed" in method and variable names to avoid confusion
with the ``raw_url`` key in the datasource mapping dictionaries.

Addresses https://github.com/openelections/core/issues/125