auto submit when file is clicked in SingleChoiceMode

[angelkoh]

Is your feature request related to a problem? Please describe. Currently, the user needs to click "Done" after selecting a file when singleChoiceMode = true

Describe the solution you'd like create a flag setAutoSubmitWhenSingleChoice, which will auto submit when a file is clicked.

Describe alternatives you've considered when the flag is set, then the 0/1 label at the toolbar is redundant. ideally, provide an option to customize the text. e.g. "Open PDF file"