Multi-select dialog with checkboxes to handle repeated answers

[joiskash]

Is your feature request related to a problem? Please describe.
This feature is to help render questions with many answer options in a nice and compact way more details can be found in #216

Describe the solution you'd like
I would like to implement a Dropdown with checkboxes to allow selection of multiple answers. I have found a 3rd party library that does something like this and would like feedback on this video , please watch from 0.39 .

Points to discuss are whether the selected options should be displayed while the drop down is closed?

Would you like to work on the issue?
Yes

FYI the video is for illustration purpose. I am not planning on using the same library.

cc: @fredhersch

Estimated date of completion 9th July