--force should be smart based on preparation type

[antgonza]

Currently, when you force a download, it forces all preparations to be that specific data_type and it will be convenient if the force was per data-type. In specific, study PRJEB21933 (https://qiita.ucsd.edu/study/description/15239); has 2 preparation types: Amplicon and Metagenomic. If we force download as 16S both get assigned that data_type, while it should only apply to Amplicon.