make dataType as an option
Merge pull request #6 from wecapslabs/data-type-option

Make `dataType` as an option
remove file model from files collection if user clicks cancel or clear button
Merge pull request #9 from xinminlabs/remove-file

Remove file model from files collection if user clicks cancel or clear button
state is done, fix typo
collection remove file is not necessary
retry uploading when error