Fixed 'rake export:speakers' to optionally specify the event slug to dump data for.
Fixed 'rake export:speakers' to optionally specify the event slug to dump data for.

osbridge/openconferenceware,ondrocks/openconferenceware,mynameisfashanu/openconferenceware,ondrocks/openconferenceware,mynameisfashanu/openconferenceware,ondrocks/openconferenceware,mynameisfashanu/openconferenceware,ondrocks/openconferenceware,mynameisfashanu/openconferenceware,osbridge/openconferenceware,osbridge/openconferenceware,osbridge/openconferenceware