[cwapi] add previous period count to count for term api
[cwapi] add previous period count to count for term api

sunlightlabs/Capitol-Words,sunlightlabs/Capitol-Words,sunlightlabs/Capitol-Words,sunlightlabs/Capitol-Words,propublica/Capitol-Words,propublica/Capitol-Words,propublica/Capitol-Words,propublica/Capitol-Words,sunlightlabs/Capitol-Words,sunlightlabs/Capitol-Words,sunlightlabs/Capitol-Words