Add dates to guinea csvs

[cmrivers]

Add the report date as a column in all digitized sitreps from Guinea. cc @pallih

[pallih]

That would be good. Name it 'Date' or 'date' and in conformity with the other files. The files in question:

https://github.com/cmrivers/ebola/blob/master/guinea_data/ebola_guinea_%2007Sep2014.csv
https://github.com/cmrivers/ebola/blob/master/guinea_data/ebola_guinea_31Aug2014.csv
https://github.com/cmrivers/ebola/blob/master/guinea_data/ebola_guinea_30Aug2014.csv
https://github.com/cmrivers/ebola/blob/master/guinea_data/ebola_guinea_27Aug2014.csv
https://github.com/cmrivers/ebola/blob/master/guinea_data/ebola_guinea_26Aug2014.csv