add an optional final report to dict_sweep helper function

[newgene]

utils.dataload.dict_sweep is used to:

Remove keys whose values are ".", "-", "", "NA", "none", " "; and remove empty dictionaries

It's quite powerful, but could be potentially dangerous to remove some fields we want to keep. So, it would be nice to have a final report at the end of its run, something like this:

<na_value_1>: 
     - <removed_field_name_1>: cnt_of_removed_values,
        ...
<na_value_2>:
    ...

can add a new report parameter to this function, default can be True.

Also worth checking if setting to True will significantly increase the processing time in a typical data plugin, if that is the case, we might set default to False and use it only if needed for debugging purpose.